It isn't than I don't think Vasturia and Beachem were poor leaders. They really developed in that area, especially Beachem. Colson once said VJ was not quiet at all even though everyone in media thinks he is, and Farrell said he was "ten times" more vocal by the end of the season than he was at the start.
1. Neither senior was given to a lot of emotion on the court.
2. It's hard to be an exceptional leader when performance on the court is inconsistent.
Colson is not lacking in either of those two categories and he has developed in the other traits good leaders have. I didn't consider him great leadership material a year ago; but after watching him grow this season, I think he will be really good at it.