no he isn't, he wasn't even here.
CB has been a problem, but so has Vinnie being injured midway through seasons when we've given him another chance.
Hazard couldn't happen because of directives from the top that we won't play the agents game, when you live by principles you'll lose out occasionally. Van Persie wasn't him, Sanchez puts other considerations first, Dybala is him listening to Pellers and is a colossal error considering we bought Bony, Laporte showed loyalty to Bilbao and also felt more comfortable with being there through his injury recovery, not much anyone can do (considering he didn't go elsewhere either).
You can't replace Yaya, you can only build a different team. Kolarov and Zaba will be done this summer but we had more urgent needs in previous seasons and we may have misjudged the odd signing, but especially last summer there was no-one really available of our calibre. Kompany has been given extra chances because why replace him unless you have to? We've also tried (after Mangala) to get the best, and they're very difficult signings to pull off who have stayed at their current clubs. Hart was replaced, it just hasn't worked yet but there's always next season, and that was Pep's choice.
English tax, Bony & Mangala are the overpriced problems, it's always going to be that way unless we sell stars, many of whom we kept hold of during the re-saleable period and thus aren't worth much (bar Kun). We've received perfectly reasonable fees for who we've sold, we just haven't sold people that important.
The club will sign who Pep wants after we've prioritised based on our budgetary constraints. If the new signings don't work, it's down to Pep.