Well, you believe what you want to. I for one think he is wrong and he has not completely master it nor ever will. I think Sasuke will, one day, attain a 4th dot and claim that title of Sharingan Master. Anime folks always seem to like doing that, stepping up and raising the bar, so it wouldn't surprise me in the least. It'd be pretty far in the future, of course.

Edit: For anyone that caught it, I do not think he'll get a 4th EYE. That'd be too freaky =/