You can say the same thing with all of the characters with the exception maybe of Jennifer. No one is being written as breakout. Only the X-Men do in-depth characterization and that's more about who's sleeping with who and what outfit you're wearing to the ball. And even then it's only centered around 7-8 characters. Even if Aaron wrote an inspirational T'CHalla in the Avengers, there's no guarantee that it will translate into a solo comic. It's up to the writer and editor of the solo to inspire interest and acclaim.
If we had a competent BP solo book out, doing all the things we wanted then we would look so hard at Avengers to fill that void. Quite honestly, I want BP doing feats in Avengers while the solo gives me characterization and feats.