It's true that Sasuke has probably done lots of training that we haven't seen. Look at all the anime training filler they've added for him. We don't watch him 24/7. And yeah, we saw him under the tree, but I'm sure he did move from there at points, unless he lived there. *Ahem*

It's true that he has natural ability because of his limit and natural genius. But I'm sure this doesn't stop him from further training. His thirst for vengence drives him on. I'm sure his defeat at the hands of Itachi only strengthened his training need.