Fedor's biggest strength was fighting in a roped square. After the fall of PRIDE, fighting in caged octagons became the overwhelming standard for MMA. Fedor refused to evolve with the standards of the sport and stuck to fighting in roped squares for years.
When Fedor fought middleweight Matt Lindland, we saw one reason why he was so adamant about continuing to fight in roped squares. It allowed him to cheat by grabbing onto the ropes with his entire arm. The referee in the Lindland fight told Fedor at least 10 times to "let go of the ropes" and tried to physically remove Fedor's hand from the ropes, but Fedor just ignored the referee and continued to cheat.
In his early thirties, Fedor finally got with the times and made the move to fighting in caged octagons. He was thoroughly exposed in 4 straight fights. Instead of evolving his game and adapting to the caged octagon, he went back right back to fighting in roped squares on the regional circuit.