What you’re saying is similar to saying that a traditional striker in the style of TKD or Karate will be neutralized in MMA. We all know the word “mixed” so it’s all about who’s the best at putting it all together. Two things:
1. It’s easier for traditional strikers to transition because fights start standing and it’s already in their realm
2. “Pure BJJ” guys like Maia have a hard time using their strikes to set up takedowns, and he is one of the least evolved fighters in terms of striking
Guys like Werdum and Ortega are pure BJJ guys but use their striking to round out their game. Then since you don’t want to be on the ground with them, you keep it standing and then they finish you with strikes. The best guys use their BJJ to keep fights standing and use their striking to get it to the ground and use their Jiu Jitsu.