Our starting 11 for the derby will be Ederson Walker Akanji Stones Ake Rodri Bernardo Kdb Mahrez Grealish Haaland. Clearly Pep wanted to rest all of them (Grealish being subbed and Walker playing as CB which is less demanding). I think his tactics were terroble against Chelsea, but today I(and anyone with two brain cells) would've selected the same players.
If your bench is not capable of beating Southampton, then that is a problem. What today showed is that we don't have squad depth and we won't win the Fa cup, but I still think we will win PL and UCL. People will act here like this is the end of the world, but every team in UCL has had rough patches this season.