I don't think genres are an issue. That could come off as a fan made quota theory, and Ultimate has done a great job in smashing fan theories (too big, irrelevant, competitor character, dead series, licensing hell, etc).
Also, technically 4's DLC had 5 out of 7 characters from RPGs. So its not impossible for the pass to be RPG heavy. That's also the side effect of Square taking so long to play nice. Many fan favorites are tied to them to some degree.
Plus, the Smash fanbase will complain about anything. People act like Banjo being added is flooding smash in 90s nostalgia, despite only having 2 other 90s characters.