What all these managers did have was a lot of experience being part of truly elite, high-performing club environments, whether as players or assistant managers.
Arteta was a key part of Pep's staff from the start of his tenure at City in summer 2016 until December 2019. He was part of building the centurions and saw the standards it took to achieve and maintain that level.
Mourinho was assistant to Robson at Porto and Barcelona and then to LVG at Barcelona. Those teams won a massive load of trophies, had some of the best players in the world, and competed at the very highest level.
Pep and Xabi both won everything as players and competed at the very highest level of football for much of their careers.
I think that's what you worry about with somebody like McKenna. To the extent he had formative experiences within a big club environment, it was a dysfunctional environment. That's the sort of experience that gives you insight into what not to do in terms of how a club is run, the type of culture you need, how the relationship with players should work, etc. While that might be valuable, its probably not nearly as valuable as having a deep immersion in a successful environment with a club competing at the highest level.