anyone truly awesome @ 3v3's should be able to learn most of the tricks of 1v1 in a couple games tho. Many are identical tricks from before, some are new (like speed stacking early to get flags / creeps faster and completely avoiding battle until much later). I know I've personally learned several things from 1v1 that I didn't know from 3v3 and it made me a better 3v3 player (and vice versa).
I don't know if I would say that they're a much better player in that case, but, I will say I've generally learned the absolute most when I lose a 1v1 game.