I was worried about the centre back situation. Relying on Kompany was a huge gamble and I have never rated Otamemdi. He is too rash and too quick to go to ground. It's fine if it comes off, looks great in the highlights, but if it doesn't he's left on the floor and the attacker is away for a one v one with the keeper, or he's given away a free kick in a dangerous area.
Watching us this season though and I can see why Pep was more relaxed about the defence. We start defending at the front and often win the ball back high up the pitch. We defend as a team and limit the opposition to very few chances. We did the same last year, but the big difference this year is having a keeper who can actually save a shot. Last season Bravo let in almost every shot on goal.
The new fullbacks made a difference, but the biggest difference is Ederson and having a keeper who the defence have confidence in.
Even if Stones gets injured, I honestly don't think it will be as big a defensive crisis as you think.