Ideed, actually in the UFC, 1,2 and 4 Royce Gracie showed to everyone how useless all these Jiu Jitsu basic fundamentals does not work.
May be you need to ask your self why great jiu jitsu and fighters like Demian Maia, Gilber Burns, Ronaldo Jacaré, Chales do Bronks, Roger Gracie, Nate Diaz, who successfully adapted their Jiu Jitsu for MMA, consider essential to train jiu jitsu with GI in every camp.