In his 5+ seasons as Utah's DC, Sitake has had numerous more players make NFL squads (drafted or not; either way a reasonable measure of player ability coming out of college) than from BYU (under Bronco at D) at the same time. Given the two schools have recruited similarly during that time frame, that suggests he is a superior coach in terms of player development than Bronco. And if you argue he had better recruits to work with, that also gives the nod to Sitake's defensive system (which is what recruits look at) over Bronco's.