I think the debates lies more with when people ignore the context of some of those managers and ignore Pep's good fortune. Pep inherited three of the greatest players of all time at Barca (Xavi, Iniesta, Messi) . What he did with Barca is incredible, but boy did he have a good (if previously underperfroming) squad to work with. He then goes to Bayern, which until recently is basically a one team league, and he actually fails to win in Europe with them. Then he goes to City who have infinite wealth and strong accusations that they've cheated for a long time. Again, his achievements are great but on closer inspection, it's not exactly a miracle is it? So you see, Pep has been a great manager....but he's never crafted something that needed a lot of work and with limited resources. Now lets look at some of the others:
Sir Alex- won a European trophy against Real Madrid with Aberdeen....Aberdeen
!!! Goes to England where he then builds up a United team that takes a huge amount of time to get going, he then has to rebuild the team another few times over a twenty year period, and never once falling lower than a third place finish in the league during the premiership years.
Jose- wins the champions league with Porto (!!) goes to moneybags Chelsea and breaks up the Sir Alex and Wenger hold on the league, and then goes to Italy and wins a treble with Inter. The Porto and Inter achievements are very impressive.
Klopp- Actually wins leagues with Dortmund on a fairly tight budget, and with his players often 'stolen' by Bayern or other bigger clubs. Moves to Liverpool who have been a joke in the league for most of the premier league era and just completely rebuilds the club, wins a champions league and premier league and is two games away from a quadruple.
Do you see why some people think Pep has had it a bit easier? You can say Jose or Klopp spent big at times but at Inter and Liverpool they made a huge profit selling big players and buying brilliantly (think Ibra or Coutinho sales and buying Eto and Alisson).