Only counting dunks is a very narrow view of "going to the rim with authority" and, while Jahmai's dunk yesterday was sweet, I'm not even sure Jahmai has more dunks this season than Julian. I think we can agree both players game thus far has emphasized attacking the paint vs. shooting jump shots or 3's. Therefore, free throw attempts should be a good indicator of who is initiating contact and attacking the paint. For this stat, Julian leads the team and is WAY ahead of Jahmai (9.5 vs. 2.2 on a per 40 min basis).
Edit: This is not to say I don't love what Jahmai has been serving up to go along with his mentality for the game and athleticism...I think he is really going to make some big plays for us this season at key moments.