That's generally the case, yes. However there is some evidence that a very small number of managers or coaches do actually make a difference (eg Clough, Ferguson, Wenger).If managers didn’t matter then why do clubs change them so much when things go wrong as surely by your logic, it wouldn’t make sense to sack someone and then appoint someone else as the outcome will be the same?
So the right strategy might be to change managers often in the hope you eventually get one of the few good ones.
Even if that is the case you need to give managers a fair amount of time to make sure you've not already got one of the good ones and even then whatever edge they have might not last. For example I think Wenger's early success was due to him being an early adopter of player data analysis. Once everyone else had those tools he stopped overperforming.
Anyway, if you think the data show that Klopp and Guardiola are doing better than expected, given the wealth of their clubs, feel free to publish it.