Fair enough; that's mainly been scourge and Saithor.
I get that. Though with examples such as Batwoman, diversifying the heroes can be done by writing new heroes who are already diverse; I would contend that the tendency for them not to “stick” has less to do with them being diverse and more to do with them being poorly written. You mentioned Bunker earlier: the problem that Bunker faced was that Lobdell's Teen Titans in general were poorly received. Bunker was actually one of the better written of the group. But the overall quality was so bad that it weighed him down. If we were ever to get a YJ Volume 3, I wouldn't mind Bunker being on the team.