ThreadMin Min revealed as ARMS rep in Smash Ultimate
While there is definitely an issue with the industry as a whole, this is a conscious decision on the part of Sakurai and the Smash team. That's something that should be acknowledged as well. There are characters that they could have added but didn't. Twintelle is just the latest example, and a big part of the frustration is because she seemed like our last chance.
For example, I'm not sure why Fire Emblem has so many damn reps, and we didn't get, say, Urbosa from BotW despite Zelda being one of their tent pole franchises. She isn't black, but she would have fulfilled some positive dark skinned brown representation (which is also very under represented in Smash). Even if they had to go with FE:TH, Claude could have been a viable pick too. We could have gotten Elma, or even Marina. People will make excuses for why these characters didn't get in, because they always do, but let's be honest and say that Sakurai could have picked them if he wanted to. We got Cloud Strife even though he hadn't appeared on a Nintendo system at that point, which was a supposed rule back then.