As I said, I can understand why it is questioned if his system is the best for the CL although personally, I'm convinced it is. This competition is just incredibly hard to win due to the luck factor in KO competitions.
That being said, the teams you mention all have the real difference makers in world football. Guys like Cristiano, Messi, Neymar and Mbappe. Look at the last 11 years. 5 CLs went to a team that featured Ronaldo, 3 to a team featuring Messi, one to a team that had prime-Robben and Ribery. The only exception is Chelsea and they fluked it.
Oh and by the way, of these 11 titles, two were won by Pep himself and another 6 by coaches/teams whose systems were heavily influenced by Guardiola himself (Zidane's Madrid, Enrique's Barca, Heynckes' Bayern).
Thing is, in order to win the CL you require luck. Much luck. When City and Liverpool meet, I'm sure most of us will bet on City if they had to choose. They are just a better team and would probably comfortably win a match up consisting of, say, 10 matches. Yet Liverpool won the CL, not City. Isn' that prove enough that the CL, though the most prestigious trophy in club football, is a badeasuring stick to judge the quality of a team and managrr?