Well this was his 10th UCL with City if I am not wrong and he won just once. That is not easy obviously for the fans because we all can see that they are a great team, along those periods he won something like 6 or 7 league titles, right?
I mean even other teams like Chelsea and Liverpool won the UCL during his stay here, and City won equal amounts as them, which makes it very questionable situation. He makes the team so good that you expect them to win UCL, and then he ends up losing, which is the reason why he looks like a failure at UCL. Normally if they weren't this dominant at England then you wouldn't question other stuff neither, but you do look at them at premier league and then how they fail at UCL and I think it's clear there is a stark contrast.
Pep is one of the best coaches in the world. According to many, he is the best coach of all time. However, despite bringing a lot of success to City, he has repeatedly failed to win the UEFA Champions League. The team that won the Champions League in 2023 was an extraordinary team. In defense, Dias, Akanji were all in great form. On the other hand, the midfield with KDB, Bernardo Silva was almost unstoppable. Along with Haaland and Rodrigo were also in their best form.
However, City's team was quite strong in the rest of the Champions League seasons. Even then, one of the reasons for the loss was that Pep got nervous in the final and changed tactics. That could be a big reason. It would be wrong to blame it only on luck.