Indeed, actually in the UFC, 1,2 and 4 Royce Gracie showed to everyone how useless all all these Jiu-Jitsu basic fundamentals dodoes not work.
Maybe you need to ask your self why great jiu-jitsu and fighters like Demian Maia, Gilbert Burns, Ronaldo Jacaré, Charles 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.
Your argument is so absurd as saying that pure wrestling is not effective because when training single and double legs, they do not take into account flying knee on the face...
I recommend you to watch the fight: Minotauro vs Bob Sapp. In this fight, Minotauro use the most basic jiu-jitsu to defeat Bob Sapp who outweighed Minotauro by 127 pounds.