This has been a long-running point of discussion with @BwdYeti, whose opposition to the split can be stated thusly: mages have no use for strength, and melee units have minimal use for magic (beyond enchanted weapons, which are highly uncommon). Splitting the stats offers no benefit other than the creation of hybrid classes, in essence (but those would account for maybe 10% of the class selection at best). Here’s a chatlog dump if anyone’s interested, where we considered a gaiden-style MP penalty system to put Mages’ strength stat to use.
The “Tellius solution,” which was once tested years ago in FE4: Advance, made strength the stat buffer for weapon weight. This original str/mag split made luck a static stat to replace constitution, and then revamped the original luck into the new magic stat. However, that makes high strength units even more OP. At base, after making the switch, Noish doubled just as reliably as Alec - which a static constitution stat balanced.
The dream, of course, is to just add the new stat outright, thus preserving constitution. But what use do mages then have for strength? It seems like an interesting design question to tackle, so I’ll pose it to the community.
Yetiman says this problem can’t be solved, but maybe someone here has some insightful commentary?