I think the reason why people complain (and without understanding and being kind to the good voices in their fanbases, which is unfair) about FE and Persona versus their own picks (and vice versa) is because of people growing up with varying gaming landscapes. Ones that aren't as memorable or lovable to them or even never experienced are ones they may particularly cast a discerning, judgmental eye at. A lot of fans of big JRPGs may be like this because they are used to the fabulous (trust me, I agree, I LOVE P5 and Royal only made it BETTER) hours and hours and hours of content, extremely rich lore, and stuff that a game like SMRPG doesn't have. It goes the other way around, too, as I know some SMRPG super fans who just don't care for massive-scale JRPGs like that.
The truth of the matter is this: sweeping generalizations on BOTH sides aren't cool, but it is a little understandable to see that gamers come in all shapes and sizes. The variety is tremendous, and when Smash is a convergence of all sides of gaming, there are sure to be conflicts of interest. Some people handle this with maturity; some handle it with ridiculous harassment and painting groups as 'bad'. It can get pretty black-and-white and petty, and it's one of the fanbase's worst problems that gives it that 'toxic' reputation. "All stale anime JRPG fans are the same vile people." "All stale bing bing wahoo fans are the same vile people." It goes both ways, and in a fandom like Smash's, it blows. The hell. Up.
Basically, it would explain why people may point fingers at FE's, Persona's, FF's, etc.'s fans, same with fingers pointed at Geno's. Does it justify it? Hell no. People need to respect what gaming means to them, because with how gaming is so WILDLY different across the board, one person's heartfelt experiences and affections are another's idea of the bland and meaningless. Unfortunately, it means that with a huge crossover fanbase like Smash's, it's par for the course. It gets really bad sometimes, too. The amount of people I've seen doling out death threats to both, say, fans of Byleth AND Geno alike is much too many. Over a video game.
It's not the separate fans and groups that are the problem. It's the unfortunate lack of respect from parties within those bases. This includes the 'anime fanbases' and our own. No matter from whom it is, it is all immature, petty, and hurtful, and needs to be fought against. The beauty of gaming is how massive the pool is, so let's not beat each other with our pool noodles because people prefer a different color to yours.