It’s nice of you to provide lots of info; if anything, I’d argue that you didn’t put enough! I feel like there are a few things you need to answer before we really begin to devise a solution. I had to take some time to really formulate this reply and help as much as possible.
-First, what’s the story behind this chapter? I know you’re probably thinking more about gameplay, and you should, but without even the slightest bit of explanation as to what is going on, you won’t be able to convey objectives easily to players. Why has a whole town of green units decided to join the fray? How are they relevant to the main party’s quest to seize the gate? Another thing you need to note is when this chapter takes place: is this early, mid, or late game? This is really important as you need to make sure the player doesn’t accidentally make the chapter unwinnable for themselves. I’ll assume that this is early game since you don’t seem to have many units at first (until the green units [henceforth referred to as the townspeople to differentiate with the outside party] become playable). I’m also guessing that time placement doesn’t matter much to you since you’re already taking lots of Thracia 776 cues (anything can happen!), and while there’s nothing wrong with taking a vision and actually going through it, consequences be darned, even FE5 (for the most part) [1RNG? Based.], you should at least try to hone in on what made this vision work in the past and what parts of it didn’t work or at least didn’t age well. This is something that’s going to be a repeating theme in this reply.
-Second, may I ask why you choose to have a 7-turn limit? Vanilla and other fan games usually round things out at 20 turns, but here we see less turns than a darn defense map, an objective that normally does not require you to move around as much. There really needs to be a good reason to justify this, as the more constrained you are, the more the chapter resembles a playable cutscene. Even linear maps need to have some loose leeway to allow for different experiences and narratives. I see that you’re already making efforts to fix this by putting a village in the northeast, but let’s save that for another part. I know you said that you yourself don’t believe that the turn limit itself is impossible; as you demonstrate, it’s not impossible with an invested team.
-Third, you need to be more obvious when it comes to conveying important information. Some info doesn’t need to be said since the player is (and should be) already acquainted with things like long-range bows from previous chapters, but important chapter events like the castle gates opening need to be divulged. The classic “show, don’t tell” is really an overrated tip. It’s necessary for books since despite being capable of non-linear narratives, they are ultimately linear in how one interacts with them and keeps track of things. Video games, on the other hand, need a lot more set up. They are an interactable interface that constantly requires input, even if it’s “just” moving 0s and 1s. Telling is just as important as showing because some types of information rely on the player following responding to them. FE4 and 5, the games you intend on emulating, tend to seesaw on how well they balance showing and telling. For example, FE4 doesn’t have to make you watch (20 year old spoilers, but since you almost definitely played the game, I probably don’t need to do this) Arvis and all of his cohorts using Meteor over and over on Sigurd’s allies. No, they just make up a fancy cutscene and then cut to text scroll. Nice and quick. On the other hand, watching Travant’s men hound at Quan’s HP over and over while Quan is heading through the desert is just tedious and boring. Yeah, we get it, he’s gonna die. Then there’s Metroid: Other M, a game that relies too much on showing and not enough telling. But I’m getting off-topic. Have a brief conversation the turn before the gates open where a guard orders them to be raised. Or maybe when the map begins. Even Thracia 776 at least has the courtesy to explain most of its inane map gimmicks except for those idiotic warp tiles to the player.
With those out of the way, let’s focus on the meat and bones.
-I take that the spot held by the druid on the north is the seize point since the “gate” in the south of the town (as well as east) opens up. (Since the house to the southwest of the city has a tile called “gate,” it might throw off some players.) What is stopping the townspeople from just bomb-rushing the druid and then wait for the lord to arrive? From how you structured this, I presume that the townspeople are intended to be a tad too weak to beat the boss, requiring the player to bring the outside party to the city and handle things there. This is a bit wonky considering how if that’s the case, the townspeople would probably be significantly lower-leveled than the player’s main force and thus would need more investment just to keep up. However, it appears that you can still have a reasonable outcome fighting the druid with Wyatt, so at least there is some sense of balance. While not particularly a bad idea in itself to give the player multiple options to solve this problem (which is great design, by the way), here in this map, it almost feels like you’re just playing two maps at the same time. Again, it’s not unprecedented (and it definitely feels like it’s on purpose since that’s FE4’s schtick), but usually stuff like this relies on events on one side of the map affecting the other. Most of the reinforcements are solidly directed towards one zone or the other, which doesn’t help things at all. Speaking of reinforcements…
-Better reinforcements. I’ve noticed that you yourself don’t seem to like your reinforcements. But again, sometimes telling is better than showing. Usually, reinforcements are positioned at the edges of the map or on obvious places like stairs, fortresses, etc. However, I noticed that you expressed your anger at things like the lone Bow Knight coming from the south. Are you mad because it’s a promoted Bow Knight or because it spawned from the south area when it logically does not have much of a reason to do so? At the very least, decorate the area with a small path. There’s also the Wyvern Rider coming in from the west forest. It’s not that big of a deal since it’s a very inaccessible place, but even considering how close it is to the southwest house, what purpose does it even serve beyond making life harder? Like, really. The southwest house is already a distraction, so why have another hurdle on top of it? That item you were talking about had better be good.
-You point out that there is a house on the northeast. However, while it’s a good step towards adding “diversions” towards a time-limited map, it’s simply far too away, even taking into account the players’ increased movement. A one-round trip to that house would require at the minimum two turns, which is already a significant chunk in the 7-turn limit. Said house also looks a bit plain and shabby even when compared to the other featureless houses. If possible, give it a different color! Remodel the road to have a path leading to it! Do something to make it stand out more. You already made the southwest house look distinct enough; what’s wrong with this one?
-Oh boy, 2-3 range archers and 3-5 range archers, too! Definitely a controversial subject, so much so that a lot of people retch at just the thought of the former (Project Ember, anybody?). Your archer already has a 2-3 range bow, so that’s good. 2-3 range archers tend to be controversial since in practice they tend to be 3-range units due to players wanting to avoid as much damage as possible. While the enemy archers will probably have to be that way due to geography, said geography may be seen by the players as giving said archers an unfair advantage. Of course, that’s what you want, but considering how much you have to snake around just to kill them and make the path safer, you could maybe shift the entire geography of the section a bit more west to make it a risky shortcut, to say. This presents a choice to the player: do you want to take the safer but longer path or the riskier but shorter and XP-filled path?
-My own suggestion: during the story cutscene leading up to this point, have one of the townspeople sneak out of the city. It could be Wyatt since he’s an assassin, or someone else. My point is: have a straggler from the townspeople escape and run to the lord, explaining that they need help. “Stragglers” who have escaped a precarious situation and need help to free their friends are no strange characters in Fire Emblem, and they serve as a medium between the lord’s preexisting force and their own potentially less powerful allies. This serves as a benchmark to help players analyze their own team and think about whether they have trained up properly. More importantly, this can also provide a failsafe to help clear the map more easily. Replacement characters, especially like those in FE1-3 and 5, are well lauded for this attribute. It would be pretty funny if the escapee was also an archer with a PRF 3-5 range bow, but that’s your call.
-Suggestion number two. While you have talked about considering nerfing the levels of the enemies, remember this: quantity is a quality all by itself. Enemy formation is just as important as levels, weapons, skill sets, etc. This is something that we have to figure out by ourselves (“draw the rest of the owl” meme intensifies). You’ll have to experiment with enemy formations to present challenges to your liking. Mix it up a little bit, and this especially applies with reinforcements.
I’m obviously far from the most qualified to give feedback, especially when it comes to enemy placement, but I really hope any of this advice can help you. If you have any other relevant information that could be useful, don’t be afraid to tell.