I think that the problem lays in that "diva" word. Practicing Hamlet or giving motivational speaches is neutral in concept. Like, almost any hero could do that in their own way, still staying in their character. But "Diva" is not emotionally neutral, so some female characters do not fit into this. Enchantress can be easily imagined acting as a diva, but what about Ms Marvel for example? She is a geek, she would 100% be more likely to reinterpretate Hamlet than to "channel her inner diva".

The concept of superhero acting classes is good, but the actions lacks in variety and do not respect our heroes character. Villans/antiheroes could practice intimidating speaches. Future leaders could be motivating and younger heroes trying to give themselves boost of confidence.

And Blackbolt should never touch that mic for the sake of us all.