Just as most other people have said there, Archers are mostly bad due to their low base stats (in GBA at least). Most prepromote Snipers have good enough stats to actually do something (see Klein and Innes). Simply said, giving them better base stats on par with your other units or higher than them allows them to be useful and actually contribute instead of being an high investment machine.
As for Snipers however, I think one should give them something special to make them worth training up for. The main reason why I think that way is because Snipers are the only Infantry class locked to one weapon without any special thing to make up for them being locked to only Bows. They are practically axeless Warriors, which is why I think Warriors would be more preferred for a bow user once you really get to the point where your units promote, since they do tend to have better strength and as such, better chip damage.
So, what do I suggest for Snipers?
I think they should be given either Bowrange +1 or Crit Boost. Either one of them gives them something to make up for bowlocked, though both come with a problem:
Bowrange +1 has the potential to cheese bosses with 3 range and can break certain maps due to them being able to attack from 3 spaces (or 4 with Longbow), so one should account for that.
Crit Boost is a simpler alternative, as that gives them something to stand out and be on par with warriors. However, it can also be an issue, as Snipers do tend to be one of the first promoted enemies, and generally speaking, some of the most common enemies the player faces in FE Games and Hacks due to their weakness of being unable to retaliate. Their aditional crit would make them a problem unless the player has a tanky unit with enough speed to not get doubled by them, have a Hoplon Guard by that point or if Snipers wouldn’t appear as early promoted enemies. Crit Boost is one of the reasons why Swordmaster and Berserkers are rather rare as enemies in most cases, so you’d need to account for it properly.
Bows themselves are quite alright, though I prefer to give them axe might or might higher than axes (thus making them the most damaging physical weapon) to make them more useful and make enemy archers more of a threat, being able to dish out huge damage to make up for the fact that they won’t survive after their initial attack.
Lastly, if you want to fix Archers, you should make the game more oriented on Player Phase combat like FE6 or FE11 than Enemy Phase like FE7 or FE8. Archers are bad in the latter two since theres really no reason to use them when the game throws loads of enemies and reinforcements at you, which your Paladin can easily wipe them. Sword users suffer too from that, but that’s not the main point here. Make enemies an actual threat, while spamming them less. Quality over Quantity is always preferable.
In Short: Give them actual stats, give Snipers something good to stand out, doesn’t need to be Bowrange +1 or Crit Boost, just something to not make them axeless warriors, maybe buff bows a bit and make the gameplay actually favour them