Ahem.
No genre is under-represented in Smash, just like no OTHER markers are under-represented.
We do not have quotas for representation, only characters people really want. That's the only quota: characters that fans really want.
Oh, and looky-here! People REALLY want more JRPG/RPG characters despite all the RPG characters in Smsh already. Isn't that weird?
Geno, Mallow, KOS-MOS, Lloyd, Yuri, Velvet, Sephiroth, Tifa, Sora, Crono, Neku, Rex & Pyra...and SO many others. They are all requested because people have fallen in love with them and the game was crafted around making that happen, where as with other games the game doesn't really have the goal of doing that. I will say that some games that aren't RPGs do dedicate themselves to a good story and having good characters, Master Chief being a good example of this. Fighting games often actually have over-arcing stories for the characters that mostly get lost in the shuffle for those not looking for them, but are actually rather well fleshed out. I've noticed that action-adventure games and hack n slash games are doing really well for character stories and development when they never REALLY did that as much as they focused on fun action.
Overwatch and TF2 do not compare to any of what I've listed. I'm sorry, but having quirky characters with small film segments that hint at more is no where near a fleshed out character story that has multiple arcs. That's not to say you can't like those characters, but when you compare those who love Tracer to those who love Cloud, you can tell which character is more deep and has more dimensions to them almost immediately.
There are multiple reasons for wanting characters in Smash. Personally, I see the FPS hype to be more about a playstyle that hasn't been in Smash all that much and even MORE about genre representation (which, as I mentioned, doesn't matter in the grand scheme). The playstyle part I can get behind, as I support Incineroar's inclusion, even though I feel like any FPS character will be more about shooting different guns that do different things rather than anything crazy interesting...but if anyone could get me to play a FPS character in a game, that would be Sakurai.