Well, a "bad coach" could be someone who inherited a lesser talented team and can't make it up "in time". But I agree with your point, one can look at say Butch Jones and see examples of poor coaching pretty clearly over the years, including stupid stuff he said in public. The better coaches usually use "coach speak" and avoid over promising.
Maybe Snyder at KSU was the best coach in the country, I don't know, or Peterson at UW.
I thought Spurrier was an excellent game day coach. He didn't like to recruit. Urban Meyer won everywhere. Saban wins when at a top program at least. Dabo has earned some plaudits. One could almost just post winning percentages by coach and rank them that way though, but it would overlook perhaps a great coach with lesser talent.
I do agree it's easier to spot a bad coach than a great one.