well it was 3 years of training for Sasuke and 2 1/2 years for Naruto. Im not saying Sasue shouldn't use he sharingan only that its thanks to his sharingan that he's as tactful as he is. Sasuke's chidori variations are the chidori with chakra manipulation and the rasengan is the strongest chakra manipulation shown. Naruto learned oodama rasengan, better his summoning skills, better his taijutsu, learned how to break genjutsu, increased his jutsu timing (kakashi said), learned "that jutsu", and spent most of his training trying to control the fox. trying to control the fox is way harder than mastering the curse mark. Kakuza had 3 hearts so how was he weakened? Naruto killed 2 of his hearts then Kakashi killed his last one. Kakuza was at 3/5 of his strenght while Naruto was exhausted from his training to learn the rasen shuriken, Tsunade gave Naruto either a 12 hours or 24 hours and Naruto baerly finished and made it to the battlefield. It was hours of intense training that's suppose to take years to complete, yet an exhausted Naruto killed 2 hearts and destroyed the body of Kakuza who had 3 hearts. Sasuke can easily copy jutsus where has to take the time to learn the jutsus. Zetsu stated Naruto (Sage Mode) was stronger than sasuke (MS). Naruto enters a war and makes Kage level clones when he wasnt at full power. He started off with 5/9 of the fox's chakra then went thru intense training learning to conrol his chakra arms, tried to transform into the fox, learned more variations of rasengan, and trying to learn tbb before enterng the war and was said to use up alot of chakra before going into the war. Naruto beat the 4th Raikage in a speed match, beat white Zetsus with his new rasengans, beat an edo, fought with Itachi and Nagato, have clones (strenght splitted between them) in every battefield, 1 clone beat 2 kages with help. Naruto is exhaused from going into kage level battles after intense training and still fighting. So we never seen a full powered Naruto yet and he's going to be working with the fox soon. Sasuke (MS) couldn't keep up with the 4th Raikage and needed his Sasunoo to survive the bwhere Naruto showed he was faster than the 4th Raikage and he wasn't at full power. Full poer Naruto is currently the stronger than Sasuke until Sasukattle e shows his new powers, Im basing this as nine tail fox powerful limitless chakra is > than EMS with the proper conditions like working with the fox and and know tbb. Naruto has started to fight smarter after itachi wise word and Naruto wasn't fighting smart against the Raikage. Naruto beat 4 Kage level who weren't below half their strenght and Sasuke only beat 1 who wasn't bedridden sick, blew themselve up, planning on letting him win. They both had help in their kage fights too.