What has been happening with Guardiola for a couple of years now in the CL or to Mourinho for 5 years now is more or less what happened to SAF from time to time: ppl question your tactics, call you naive, stubborn or even overrated and expect CL trophies regularly.
Even some of our own fans have one of their favourite line "2 CLs in 26 years" and this couldn't be more wrong! Which 26 years exactly? Didn't we only win our first league title under SAF in 93? And weren't English clubs banned from Europe anyway almost prior to that? And didn't SAF immediately win his first European trophy for United (Cup winners' Cup) in the first year he actually competed in it?
So it's actually 2 CLs (or 4 finals, some more semis and reaching the CL quarters 7 times in a row in a period where the rest of PL teams were nowhere to be seen in Europe)in 18 years (1993/94 - 2012/13 minus one season when we weren't in it as Blackburn won the league in 1994/95).
So it's indeed 2 CLs in 18 years, not 26.
Could he have won more? Yes, but it's still a very good record considering in that period he also rebuilt several teams and every transition takes a couple of years.
What I am trying to say is that the longer you stay as a manager, the more the room for failure will increase. If Guardiola had retired in 2011 or Mourinho in 2010 ppl would have probably never questioned anything they had done. Because in a shorter period everything can be perfect for you, you are also perfect, the team has clicked and the luck was there in some defining moments.
But over a longer time period not everything will always be perfect, other great teams will emerge, you will have to re-build and re-motivate your team and maybe also re-invent yourself a bit and adapt because teams have figured out how to play against you, etc.
I mean also look at Di Matteo, 2 CL seasons, 1 trophy. Doesn't mean he is a genius, which was also clear when they finished 6th in the league the same season and were the first reigning champions to get kicked out in the group stages. But in that one CL season everything just worked for them in that competition.
There will be a lot of more occasions when top manager like Pep, Mourinho and also Klopp and Simeone will get things wrong. This is bound to happen in a long management career. But that doesn't mean that some of them need to be called tactically naive or overrated everytime something like this happens.