Board Thread:Theories and Speculation/@comment-32742265-20180119154238/@comment-6769189-20180210005117

Gai literally explained what he meant in the same panel. Everyone attributed his execution of it to the Sharingan.

Izuna didnt use FTG because it requires a special seal.

Sasuke doesnt copy Naruto's moves because he prefers his own and thinks Naruto's moveset represents weakness. He said so in VOTE2.

Saradas incomplete Sharingan copied Borutos Shadow Colne jutsu after seeing it just once, sooooo....