Board Thread:Theories and Speculation/@comment-32742265-20180119154238/@comment-6769189-20180210072645

Despite having copied over a thousand jutsu Kakashi sticks mostly to Raikiri and its varients because his entire fighting style is based around that. Likewise, the Uchiha had their own unique fighting style that they knew best. In all reality we only know how Tobirama/Hashirama and Izuna/Madara performed against eachother in combat. Both Senju had unique Jutsu that either required a pre-req or was a KKG. This silly argument can be applied to Naruto and why he only used Rasengan varuents even though SPSM gave him fundamental understanding of chakra and he had 9 tailed Beasts with various elements/attacks that he never used. Either way part of the reason the Sharingan is so coveted is because of its copy abilities

Sasuke didnt copy Suigetsu's abilities because they conflicted with his fighting style, made him vulnerable to his own main element, and would hamper his other element. Some of Karin's moveset was relient on her Uzumaki traits. There is also strength in numbers. There are numerous occasions when Sasuke would have died had he been alone.

Sasuke and Sarada have perfectly copied techniques they had only ever seen once and never preacticed beforehand. It is stated multiple times in the series that it can copy whatever it sees. The only exceptions specifically noted have been KKG or techniques that require specific items/contracts. It was never stated to be unable to copy jutsu of a nature the user hasnt mastered/unlocked. In fact Madara showed us the opposite by just having the potential to use wood release he was busting out jutsu he had only ever seen.