I don't understand the argument. If there is one. It's Ross opening up a debate about the importance of managers, and how in most cases, their actual influence is overstated.
I don't think anybody would deny that the most important factor in winning titles is the players you have in the squad and how good they are, which is itself dictated by how much money you have to buy the best players, and pay the highest wages. There's always a team that can disrupt that, for a short time at least - Atletico Madrid, Valencia, Dortmund, Leicester whatever, but that's always with a whole bunch of other, additional factors; luck, form, injuries, keeping your best players etc etc
And I don't think anyone would deny that Klopp is a better manager than Rodgers, but expecting him to take this bunch of twats to the title is preposterous.
Finally, while the manager is only ONE contributory factor among many, and certainly not THE most important one, it's also very true that sometimes that alchemy for whaetever reason, doesn't work when they move on. Does anyone think AM will continue to challenge when Simeone leaves? And just look at what happened to United when Baconface fucked off. So I wouldn't overstate the importance of the manager, but nor would would I reduce it to negligible.