You know the setting of SMTxFE, actually makes sense cause the devs wanted to make a Fire Emblem game in present day, and I'm pretty sure Persona is the series of SMT that is set present day. Also I love how people keep saying there isn't much SMT stuff in the game, when revealing that would probably cause spoilers, since isn't it mostly set in post apocalyptic settings
Also it was never really said that SMTxFE would be a crossover between the 2 series in the sense of a normal crossover. Plus the gameplay style their going with still makes a lot of sense to me since it does the usual RPG stuff that would be found in an RPG and its found a good way to mix in strategy elements from Strategy RPGs, since normally speaking the way that strategy rpgs handle strategic advantages, don't exactly really translate into RPG battle systems that well normally.
Also people who complain about the characters from SMTxFE being in high school is actually really silly when I think about, cause, pretty much all the protagonists of Fire Emblem are actually teenagers, and so are most of the supporting cast. Remember FE is a medieval fantasy so most teenagers in medieval times were pretty much working full time jobs when they reached 13
Well anyway I'm still not ready to judge SMTxFE just yet, since most of the stuff we've seen is apparently early game stuff, so it could still actually go very dark later on. Just like how FE can actually get pretty dark when it comes to talking about the wars you part take in in the games.