To me, win percentage is worth more than longevity. Frank Leahy deserves to be on that list more than Woody Hayes or Eddie Robinson.
I concur with the winning pct, but the more important barometer is context.
Frank Leahy coached during the WW2 era when teams were decimated by players going off to war (this affected Notre Dame, as a religious school, and Army, who was training the "leaders of tomorrow", less than other schools).
Leahy (and other white coaches) had so many advantages over Eddie Robinson that it isn't even mildly amusing.
I'm not going to say he was a bad coach but in context his record isn't so impressive.
Robinson still won over 70% of his games, and he progressed through numerous eras. You'd think that once integration opened up the opportunities so that Robinson could no longer corner a large share of the black talent that he'd sink like a rock, but he was still winning 9 and 10 games late in his career (though he held on too long as a lot of them do).
He also had the wins record for 26 years. AA Stagg might have held it for 23 years, but he also lost nearly 40% of his games and was coaching at 95 years old.
On the flip side, I appreciate you reminding us not to just get focused on the "what we've seen" aspect, either.
One could argue that Clark Shaugnessy is as important a figure in CFB as anyone else. Most folks today don't even know the name.