When you specialize in something in mma, 8 times out of 10, You will be fighting a guy who's gameplan revolves around not engaging you in that area. Not enough people really appreciate what an effect this has on the metagame of useful tactics, training, and procedures.
Take a guy like Danial Cormier for instance; in his career as an olympic wrestler, his game basically revolved around getting the tie-ups he liked, baiting his opponent into taking a shot, and then reversing them with a go behind.
Obviously, pretty much no-one has ever obliged him in such a way inside the cage.
Its not something that's ever really touched on, but he had to pretty much completely retool the way he wrestled all throughout his career to better fit into the mma metagame, which is how you can end up with situations where a guy with Cormeir's pedigree ends up getting taken down by a guy like Jones (or, for that matter, how a guy like Jones can end up getting taken down by a guy like Gustafsson).
A lot of the praxis in more contingent/'purer' combat sport rule-sets is predicated on the situation where you are contending with an opponent who is also coming together and going head-to-head with you on the same plane. But that is rarely the case in MMA, which then filters and recasts what the most useful stylistic choices from that tradition are that would be the most adaptive (usually, more active 'go-gettem' ttp's).
When specializing in something in mma, the most important thing to train is not necessarily beating other specialists in that area, but how to force the fight into that area in the fof me and toy with meirst place.