As long as Pep Guardiola's demands are met at the team he goes he is able to bring successes to that team most of the time. He has been managing only top teams maybe and we haven't seen him at a lower level team. Most probably we won't as well. However I still don't think this makes him a manager to have doubts about.
He is a very successful quality manager. He just needs a lot of money to build the kind of a team he would like.

He can find that kind of a budget at only rich teams as a result. He has finally achieved the Champions League title with Manchester City as well and achieved his main target too.
The main thing is obviously quality and then money the combination of both will bring success. If we only talk about money obviously there is no guarantee a club can win the title, in the Premier League we have one example they are Chelsea who spent €611 million last season which brings about 14 players and we know Chelsea won nothing even out of top 10 while their competitors spent less yet managed to finish in the top 4 they are Newcastle United who spent €185 million last season, Arsenal €192 million and Manchester united €243 million. If we combine the total expenses of these 3 clubs, this is equivalent to Chelsea spending last season.
Manchester City only spent €152 million last season including Haaland in it, the difference is that Manchester City has built a team a few seasons ago so they only need to strengthen lines that are considered weak or have gaps. What's surprising is Newcastle they started quickly and on a lower budget and in my opinion they deserve to be called the best club last season., they don't use a combination of money but a combination of strategy and cohesiveness. I'm curious how they are going through this new season with more challenges and schedules of course.