Arrigo sacchi is regarded as one of the greatest managers of all time.
He took over a faltering Milan team full of talent, owned by a politically influential and rich tycoon, got to spend even more, ending up with the best back 4 in history, Maldini, Baresi, Costacurta, Tasotti, and also Donadoni, van Basten, Gullitt, Rjikaard, all in the same team. 4 of those players could be considered the GOAT of their position. It is better than Pep's City and Bayern teams and is comparable to his Barca.
Despite all that talent, he only won the league once and the European cup twice in 5 seasons. After that he was a responding flop at atletico and couldn't bring home the trophy with a strong Italian team in 1994. And what of Milan, did they collapse without him? No, they won a couple of league titles and yet another champions league.
Compare that to pep's record and there is a clear winner. It's not even close. While their breakout jobs are comparable at Barca and Milan, pep has followed that with an amazing record at City. And yet sacchi is held in massive regard -because his tactics changed football. Not just did pep's Barca change football, he is also much much more successful than sacchi. There's no doubt for me that he's one of the best of all time.