Fedor is my favorite fighter ever and I dont mean to criticize him in any way but its clear that at sometime around the Mirko fight he completely neglected training his ground game.
Furthermore at that time was when his stand up looked the best its ever looked and also he had more hand injuries than ever at that point. I think all of that made him turn away from training his grappling as hard as he should have.
Defensively from his back and when on top, he could have benefited from training some BJJ here and there. I dont think he had to train to a black belt but just some nuances to help him in some moments. He was too reliant on exploding IMO however it worked well for him in his prime because of how strong he was.
When he began fighting in the US his ground game seemed to get worse and worse.The way Werdum triangled him so fast, the way he gave up position going for a Kimura and Rogers who revearsed him, the way Hunt laid on him, the way he gave up position going for a kimura on Bigfoot, how easily Bigfoot mounted him, the way Hendo slid out the back door and KO'd him from a position where Fedor should have maintained side control. This really showed very elementary grappling from Fedor from the perspective of pure BJJ. After the Hendo loss Fedor got BJJ coach from Holland who is a 17 year brown belt under Rickson Gracie. It was just too late by then.
Fedor neglected his grapppling over the years most likely due to all those hand injuries he had and his game suffered greatly because of it. This isnt to bash Fedor because he was a spectacular grappler for the generation which he came from. I was simply criticizing his grappling from the BJJ "Position before submission" stance on grappling. Hes my favorite fighter ever.