I use the classic GBA magic system, for the most part.
Dark magic is basically the same. It hits hard, is inaccurate, and has a lot of unique effects. (Nosferatu works like normal, Fenrir has 1-3 range, and a couple of new spells like ‘Diablo’ to hit DEF instead of RES when dealing with magic users.)
Anima magic is more accurate, but weaker. The only unique spell is Aircalibur.
Light magic… just kind of sucks. All of the spells have accuracy on par with Dark Magic, but worse might than Anima. However, Light Magic has been combined with staves, so clerics/priests/troubadours have a basic weak attack and Sages can level up their staff rank quickly.
I also added a new “Stone” magic type. This weapon type is based on the Dragonstones you’d find in Fire Emblem, giving you various stat boosts. However, it’s character based rather than class based.
As for the classes themselves, I usually balance them like this.
Mage/Sage: Anima magic +Staves upon promotion. A good all-around class with no real specialty.
Shaman/Druid: Dark magic +Anima upon promotion. High defense and low speed, generally better at combat than the other magic users to compensate a lack of staves.
Priest/Bishop: Staves +Dark upon promotion. Weird, I know, but I wanted a second class to use dark magic. Generally the fastest, but frailest magic user.
Troubadour/Valkyrie: Locked to staves, even after promotion. With 2 more movement than the other classes, they should be relegated to utility only.
Edit: Magic users should have a place on any team just by virtue of attacking RES since enemies usually have higher DEF. That’s without even factoring in staves like Warp and even Restore.
Also, I don’t particularly care about the lore of magic, only how it affects gameplay. The only FE’s that really make magic feel powerful, in my opinion, are Kaga’s games since units either have terrible RES or your units literally do not have RES Growths (Or both, in FE1’s case). Magic is good in the later games too, but it’s not as much of a force to be reckoned with. (Especially in the Tellius games.)