I mean, Oni also had made some good defensively stops against Devin Booker in pre-season, but then in that Clippers series he had like 3 fouls in less than 5 minutes and couldn't stay on the floor. Same with Niang, whose defensively improvement almost made us forget about his limitation. Then we saw him getting abused and walked all over in playoffs.
I think the thing with Brantly is that the idea of him is better than the real player. He certainly had his moments during all those minutes that don't really matter. But there are also minutes of him being completely lost on the floor and not looking like a NBA player. For a team trying to compete now, it'd a lot to ask the coach to play you meaningful minutes unless you have a certain set of skill that can contribute to the team right away.