Being athletically inclined in general is a pretty crucial aspect of being a fighter and all athletic endeavors have some amount of overlap or application. It really ends there, Jose Aldo didn't kick hard because of Soccer...the dude was a densely packed body if sinew and fast twitch muscle fibers.
All in all, guys are starting younger. If you look at fighters such as Cezary Oleksiejczuk he has a 14-4 amateur record and at like 22 is 10-2 pro, these Dagestanis are wrestling from 5 years old and cross over to Sambo, Judo, Sanda, Muay Thai etc as pre teens and begin their MMA careers as teenagers. Soccer isn't a good base for MMA, being freakishly athletic is and obviously having backgrounds in other martial arts and combatants is.