I think a lot of people are misunderstanding what the op is saying by dethroning Alabama. It does not mean beat them once or stop them from winning a title. Sure Ohio state and Clemson could possibly do that this year, but Bama will still get all the recruits and be back in the playoffs for the foreseeable future.
What he means is destroy their dynasty. Why USC and Miami can do that is because of their cities and recruiting areas. Bama has winning and coaching that leads the best players to them. But if Miami or USC is winning as well those top recruits will go to those places over Bama, and Bama will go back to good but not great.