Also, if you take into account the teams Pep had, he actually underperformed.
Didn't win a UCL with a very good Bayern team, and took so long to win a UCL with City despite receiving gigantic amounts of cash and violating every conceivable financial rule in England.
England has had 3 big teams in the last decade: City, Liverpool, Chelsea. Of all the three, City took the longest to win a UCL.
Ferguson on the other hand built two great teams. Once at Aberdeen, then once again at Man United, and he was able to actually sustain that greatness at United for more than 20 years, consistently. If you look at his finishes at the Premier League, what's really striking is that even when they didn't win the trophy, they almost always finished at very high positions, only one or two points below the champions, consistently for 20 years, all built by Sir Alex, with the backbone of the team being academy players for most of that period.
Mourinho and Sir Alex proved they can do it against expectations. Guardiola has spent years struggling to fulfill expectations...