Pep has never been in charge of a club that wasnt well structured. He has landed at clubs that has given him the resource to thrive.
Let me see what Pochettino does at a club like Chelsea first to make such a conclusion. Unlike pep, Pochettino has turned around clubs that does not have the right resources. Achieving things at Spurs and Southampton that no other manager has achieved yet or will probably not achieve in awhile. At Psg, he coached an uncoachable team into the champion league semi finals, won all the domestic cups, went unbeaten at home, and got the best out of a generational talent, who has been struggling since he left. I feel the platform is there for Pochettino to be in that bracket, if Bohley doesn't mess things up. If there is any coaches Bohley has to back, it is the one that he hired right now.
However, as it stands, I believe pep is going to be the best because of how his team plays and the ability to perform that way consistently over a long period of time. Moreover, the trophies he has won. Sir Alex is 1st on that list. And mourinho 2nd. But after the treble, pep will be 2nd and if pep can continue this for few more years, he will easily be 1st. But once again, let see how Pochettino does at Chelsea because he has platform now that he can truly show what he is capable of if Bohley doesn't mess things up.