You're making my point.
1) It's been widely reported that cpj was not able to hire the DC he wanted because of budget. It's possible that similar constraints affected hiring position coaches.
2) When CPJ was at GS, he often had a top D as well as O, iirc. Iow, it's not like he can't have a good D. He's discussed that in terms of not having a talent issue. Which raises the second point: having better talent doesn't make you a better coach, imo.
I'm reacting against the analysis that suggests all variables are equal except HC. I think you also have to consider context.
Imo, when ranking HCs, you should be able to answer the question, "what is their genius?" If the top two answers are hiring coaches and recruiting players, then you're talking about responsibilities that are not inherent in the word coach.