That time skip was a great excuse to add more to MC's fighting style on the spot but nope, Kishi Kishi'd it.
This.
When the story demanded it, Naruto picked up wind style, rasenshuriken, sage mode, bijuu mode and bijuu dama at the speed of plot.
Early Part 2 Naruto only had refined skills from Part 1, just to make Hebi Sasuke's growth that much more incredible. Kish wanted Naruto to constantly chase Sasuke, and not stand equal to him or surpass him until the plot said so.
Not like the story of characters in- universe ever acknowledge this though. On several occasions, Kakashi, Jiraiya, Tsunade and Obito (as Tobi) talked about how strong Naruto is/how many powerful jutsus Jiraiya taught him.
Rely on Kishi to nerf and neg things because he can't come up with better ideas of how to tell a story.