I really do believe DS's open letter impacted where the program is now. It got a lot of fans riled up wanting a change. Between Vai's constant blubbering on the radio and DS tweeting and writing his bazar open letter, I'd want to go somewhere I'd be appreciated as well if I were a solid to successful head coach of a D1 program. In fact, the only people who like Vai's interviews and DS's tweets are Yewts and Aggie fans.
Anyway, in another thread, some fans tried to say DS didn't advocate for Bronco to get replaced by Kalani. He indeed did call for the hiring of his former teammate and listed a number of reasons why, including my favorite argument that Kalani's a "complete bad" beep. In the meantime, the letter stirred the pot in a big way going off on Bronco, Howell, et. all and contributed to the sediment at the time that there were much better choices out there for BYU to hire an LDS head coach.
If you care to revisit, it reads kind of comical now, take a look for yourself. My conclusion remains, the letter did contribute to the current state of BYU football.
https://lawlessrepublic.com/2014/10/24/open-letter-coach-mendenhall-one-former-player-opinion/