Playing devil's advocate, if overrepresentation is the root of the issue, why is it that Mario characters and Pokemon characters are generally better accepted? Frequent discussions here support the idea of Waluigi, Geno, and Gen 8 representation as newcomers--with both series already having a unique newcomer in the form of
and
respectively. Meanwhile, only Chrom as an echo appeared for Ultimate before Byleth, and then Byleth was immediately considered divisive upon reveal. From this perspective, I could argue that there is a stronger apathy toward Fire Emblem than the series listed above, and it's not because of overrepresentation.
Well there's not some uniform, series-wide "cap" as to how many characters a series can get before it's seen as overrepresented. When the perceived ceiling kicks in depends both on how big the series is and at which number other series reside, which is why Mario and Pokemon, being the two biggest series, have the highest ceilings. I mean you could bump Zelda up to like eight characters and people would be fine with that, but if you bumped Kirby (or DK, or Metroid, etc etc) up to eight people would lose it.
Fire Emblem is around the same size as Kirby, DK, Metroid, etc. So it's seen as having a lower representational ceiling than Mario, Pokemon, Zelda, etc. but higher than the likes of Xenoblade, Kid Icarus, Mother, etc. Not that the ceiling is some precise, objective metric, it's all just about proportion.
So Mario and Pokemon are not generally seen as overrepresented for the same reason something like Pikmin or Punch-Out isn't generally seen as underrepresented. Because it's framed against the stature and the status of the series. It's why even just with two characters, people acknowledge Mother receives a generous amount of attention.
It's not like there's a firm equation, but you have to be a little oblivious to not see that by and large there is a rough correlation between size of series and volume of representation, with the only real exceptions being because the series is still relatively new to Smash (AC, Splatoon), owing to lack of feasible additions, or subject to intense disdain, (whether FE, KI, Kirby or Star Fox, depending on the time period). It's no coincidence that when the series is seen to "balance back out", the complaints stop.
I mean, it even exists to a lesser degree with third-parties. If you added another two Street Fighter characters, or two Castlevania characters, but left the others as is, people would start getting a little discontented. And it really has nothing to do with people hating on SF or Castlevania as series.
