No doubt with Manchester City is very strong teams right now, but current update many important player leaves Manchester City and I don't sure they will sign the same level players. İlkay Gündoğan and Kyle Walker have confirmed will leave Manchester City next season after accepting join with Barcelona and Bayern Munich, its still not stop for players leave Manchester City because Bernando Silva announced not extend contract with City and will follow İlkay Gündoğan for joining with Barcelona.
Inside Manchester City loss Mahrez after joining with Al Ahly as Saudi Pro League teams, many composition change with Manchester City next season and actually new players will need time for adapting with Guardiola games style.
Manchester City will not really lose the quality of their squad depth even though they will lose some important players. Ilkay Gundogan, Kyle Walker, Riyad Mahrez, Bernardo Silva are important players, but I think Manchester City are ready to part ways with them any time. Bernardo Silva might dampen Manchester City's strengths in attack a bit, but others won't especially as some of these players are old enough to play at the high level Manchester City demands.
Barcelona does have a good affinity with Manchester City so far, this also includes the problem of player transfers. Silva is another player who has been linked with a move to Barcelona, but I believe Barcelona would not have had it so easy to sign him if Silva not come on a free transfer.