Having 9-tails inside made lots of problems to naruto not only mentally but physically too he learns ninjutsu lot harder then most people he failed at replication jutsu 3 times in academy it was pain in ass for him to climb a tree, walk on water, learn rasengan, and he couldn't do 1 hand rasengan even after he made S class rank fuuton rasenshuriken.For Sasukes case he has sharingan lots of boosts 0 negative effects until mangekyo sharingan luckily he got transplant from itachi so he never had negative effects of sharingan he can learn ninjutsus taijutsus in a mere second look at chuunin exam he copied lees movements with only seeing it once so yes I agree with you