Guys who get kicked off of NFL practice squads -- Lesnar -- become UFC HW champ in 3 fights. Guys who get cut from the league after 1 year - Bob Sapp - beat K-1 GOATs and nearly kill MMA legends in their prime. Other NFL guys who get cut after 1 year -- Schaub, Mittrione -- KO MMA GOATs like Fedor and Cro Cop.
MMA is a fringe sport that's less popular than table tennis and volleyball. It doesn't get great athletes. The NFL gets some of the best athletes in the world.
Is it really surprising that an actually good NFL player just slightly past his prime can beat lower level UFC guys?