Honestly, one of the things that surprised me the most when playing FE for the first time was the fact that AoE attacks are scarce/non-existent, which is why I asked in the first place. I see them in every other SRPG so I got used to divide and conquering with individual units without tanking. That backfired fast on me when playing Awakening, lol.
A lot RPGs use larger numbers with less of a statistical contrast. They also generally use complex formulas.
Fire Emblem for the most part is extremely straight forward. At its base, attacks are the unit's Str plus weapon Mt minus the victim's Def for physical attacks, and Mag plus weapon Mt minus Res for magical. It uses simple, small numbers, in a very straight-forward manner. 20 Str + 20 Mt = 40 damage.
Other SRPGs generally have more formulas that are not just simple addition and subtraction. Multiplication, exponents... Generally some kind of curve and conditions. Also, generally in other RPGs, the differences in magical resistance is not as great as it is in Fire Emblem. Someone who has even a quarter of the magical resistance as someone else is still probably better off than, say, a mercenary in Fire Emblem or something.
So for theory sake, let's say you have a Level 20 Soren versus three level 20 Boyds. At level 20, if we round our numbers, Soren has 17 Mag and the Boyds have 4 Res. Let's also say Soren has two wind tomes that can hit all three of the Boyds.
The first wind tome has 0 Mt. So Soren hits the three Boyds for 17 (Mag) + 0 (Mt) - 4 (Res) for 13 damage. Even if you were to hit only two Boyds, the total damage would be so absurd compared to anything else. Keep in mind magic users are already the de facto nukers of Fire Emblem, whose damage is usually only rivalled by fighter types or myrmidons with crits depending on the victim in question. Squishy low-Def targets aside, Mages are supreme, because Res is scarce across a greater range of characters.
The second tome has a weird formula of Mag/2. Let's just do some optimistic rounding and say it comes out at 9 damage. Now you are doing 5 damage to the three Boyds, Which might sound interesting, but keep in mind Boyd is one of the absolute most optimistic targets and at that point of the game has 40 health. Three Ikes, a character who can be noted for having a more realistic Res stat, would be taking like 1 damage. Even if you wanted a really low HP target like Mia (28 HP), low HP target generally have more Res. She would only take 3~ damage.
The problem persists, even as the game progresses. For instance, at max level, promoted, the first tome would hit the three Boyds for 19 damage each, while the second would do... 4 damage to each, out of a maximum of 60 HP. :D To have AoE damage tomes, even with 0 Mt it would be unfair for an end-game tome. Something that did Mag/2 might be okay as a limited use tome you can only get a few of, though.