Just from what I've seen, mma is very pragmatic. The gyms tend to focus on what they know works. Necessity is the mother of invention, as they say. When a formula works, there isn't a lot of need to innovate. As soon as a weakness is exposed, it is addressed.
Another facet of this pragmatism, is that there isn't any thought at all given to styles that may or may not work. Wing chun, for example, just isn't thought about. If someone were to demonstrate how well it works, it would get some attention.
A third facet of this pragmatism is the acknowledgment that different and better are not necessarily the same thing. Machida is often pointed to as proof that karate works. Cool. But does it work better than western boxing? Or Thai boxing? Jury's out. So, great, we know that at least one karateka, who embraced cross training in other styles and the pressure testing required to make it work, did very well. A mma coach with an extensive background in western boxing might not abandon what he knows works in order to teach some bastardized version of what machida had studied since childhood. I don't fault them for that.
All said, I think you're seeing pragmatism and mischaracterizing is as rigidity.