The barca squad is insanely talented and they have a great mix of upcoming players, stars and veterans. Umtiti, Lenglet, semedo, Arthur, dembele, cou, alena, denis Suárez, Malcom, ter Stegen are a great group of players even if some of them will not reach their potential. For all the justified praise of city's squad, they frequently have to use the likes of delph, zinchenko or Danilo as LB. They also have no alternative to fernandinho. Every squad has some weaknesses and nobody accepts that as excuse for playing poorly. Proper management is about making it work.
There is absolutely no way to argue that psg have a better squad. City - yes; Juventus - maybe, but I disagree; Liverpool, real, bayern&co - no way. The don't have the same problem as real Madrid at all. Madrids problem is that they have one promising attacker and he is a 18 year old kid, who just joined them. The rest of their creative midfielders and forwards are a support cast that is lost without the main attraction. While their starting11 in midfield and defense might be really good, they don't score goals and the squad depth in those areas is also really poor.
Barca's problem is that they frequently play terrible without Messi. That's despite their individual quality and not because of it. Valverde isn't getting the best out of them at all. Everyone but dembele just seems to wait for Messi even if he is not on the field. It's the managers fault for not organising them properly and making bad lineup decisions. Arthur, vidal and alena all showed some really promising performances, but Valverde always goes back to rakitic, who is out of form. He has no idea how to use the likes of denis Suarez, Malcom or coutinho and dembele forced his way into the team because he is the only alternative to Messi in this turgit system.
Valverde won stuff, isn't all bad and recently they started to improve. Still, the way barca played in the first half of the season was shocking and that was clearly the fault of Valverde.