since the show is called Naruto, most of the times we only got to see the training of the main character whereas other characters do their training in secret or not shown(bcoz its not necessary). The examples are Sasuke, Kakashi and Sakura. That's the reason we think that they don't need any training like Naruto especially for Sasuke. He was not shown for many chapters in the manga and that's why no one knows what he does in the free time. Its obvious he trains in that period and then shows off during screen time and most of the fans thinks that he needs no training, he's invincible, blah blah blah.... On the other hand, Naruto's hard training is viewed by everyone and because of many failures in his path most of the fans think "He can't even do a simple thing properly". Got the difference?
Back to work : Sasuke has mastered his Enton through pure training and he's not god gifted OR Itachi gifted. The only thing is that his training wasn't shown.