better teams overall.

The overstatement some may make if the OP scenario plays out is along the lines of: "Bronco seemed to have a harder schedule his first 10 years and still got to 100 about as fast as LaVell so he must be as good as LaVell". Not so much the case. In giving the comparison a little context, Bronco inherited much better players (which significantly impacts the W/L of the first 3-4 years or more; and despite Crowton, Bronco unquestioningly inherited more talent than LaVell). From a scheduling standpoint, the program was also at a more prominent level with better non-con opponents already on the slate when Bronco took over than Lavell (largely due to what LaVell accomplished). Given both coaches had to play the schedules already set - which from an SOS standpoint gave Bronco enthusiasts an advantage of being able to say "and he played better teams" - and given that the schedules were set up very different in 1972 than in 2006, it makes strictly extrapolating W/L and making a statement about who is a better coach when based on perceived SOS tricky.

It is so hard to compare the two because the quality of regular season and bowl game opponents were a different caliber between the two, the eras they coached in were so different, and making a judgment about how "good" a coach is can be supported by almost any comparative stat you want to pull out (like how fast someone was to reach 100 games when factoring how "difficult" SOS is perceived to be.

Both coaches have done great things for BYU in their first 10 years. Bronco restored clean image the BOT wanted. LaVell introduced an exciting brand of football that led to a NC (and was a loss in 1983 away from 2 NCs). You can't really compare them as coaches, just numbers.