There are so many what ifs revolving around Pep because of his unique circumstances that really caveat his placing in an otherwise uniform and organic process. Given his resources, he has massively underperformed, because with the advantages he has always had, league competition becomes a broken formality whilst performance in Europe becomes even more important a barometer than it is for other coaches because it's the only time he faces anything like their adversity.
Other coaches have shown what you can do to a league where you absolutely dominant in terms of squad and resources - Jose did the same with Chelsea and the few times SAF was given a bigger pot to play with, our league performance in terms of both dominance and consistency took on monumental leaps. The league becomes badly bastardised when one team has humongous financial advantage over the others, so winning it becomes less impressive and every single one of the managers mentioned said that the CL became a different kind of proving ground, and it's also no coincidence all are defined by the epic battles against equivalent squads therein.
Sacchi created arguably the best team of al time when he had great resources; SAF got himself to 3 CL finals with what is recognised as our strongest ever side, breaking records along the way; Mourinho was at the helm of a juggernaut at peak squad strength, so it clearly goes hand in hand when über sides enter the fray, and one should question what the timeline looks like for any of these managers with the resources and squads Pep gets handed to him every season. No lulls, no weak areas, no chopping and changing excessively because stars leave or fade (Gullit & Van Basten; Ronaldo & Tevez), just nothing organic or recognised as pitfalls for everyone else.
It also bleeds into ideas and systems: Pep can dream up literally anything he wants in May, and by August, he'll have the majority of the components to implement it, no bother. No other coach can say the same, so for all the genius and innovation; it's not the same when you can press reset at the end of a campaign and load a new game for the next one. There's nothing organically familiar about that, and such artificial settings have to be objectively accounted for.
Pep has no storied road to the top. There's not even an idea if he could do it. Should he have had to? Well, when comparing him to managers/coaches whose biggest and most admirable feats mightn't even come at the top of their standing, but on the path leading to it, kinda, yeah. Or at least in lieu of that, shown his own journey to success through adversity, which for him is solely Europe until he faces a league side who matches his own for resources and ability to overhaul at the click of a summer window finger.
Pep is what he is, and his biggest contributions probably lay in implementation of systems that send shockwaves through the sport, but in terms of greatest, his situation is too disparate to truly be assessed in the real world - give his resources to others and they wouldn't have won less.
And ending, it astounds me the amount of people who don't understand what resources refer to when it comes to City. Simply stating clubs like United have spent 'more' whilst taking official figures as fact, that also give zero account of expenditure throughout the club in a given season. City's upkeep is astronomical, and as seamless as their operations appear to be, the amount of money pumped in to maintain that dwarfs everyone they compete with domestically, let alone when the actual dodginess of payments across the squad are factored, or not... as the case clearly is for those going by the "facts" presented to them. In game terms, it's the constant production of elite talent and constant smoothing of edges to hone the product.
