Might be wrong, but for me this is a simplistic way of thinking about a Pep defence, especially after 6 years of watching Pep's City and listening to his interviews.
The fundament of a Pep's way of defending is having a lot of possession and having a build-up play good enough to deal with intense high-pressing. For that purpose you need defenders who are great on the ball and brave in possession. Many seem to think that if we have another Walker at LB, we'd be perfect in the big games defensively wise. That's dumb. Another FB who is technically limited and chooses only save options would be deadly for a Pep build-up play and for our possession- based game. If Walker attempts to do what Cancelo does in our build-up play and in the opposition's half, he would make so many mistakes that people would question his value for the team. He knows his limitations and plays safe, unimaginative passes. If the other FB is like that, a Pep team wouldn't be a Pep team.
But couldn't we find a player who can do what Cancelo does for our build-up play (most passes in the whole league and most touches over a season in PL history, no less) and is more solid in defence? Well, where's that FB? If Cucu was that, we'd pay 80m to have him. He would be the best FB in the world by far, and one of the best players period.
If you hear or read 'Cancelo can't defend', you are dealing with a fan who watches Pep's City for 6 years now and doesn't understand how we win trophies. If we buy a FB good enough to start at LB in big games, then Cancelo will be used at RB, unless he is off form like in the final month or two in 20/21. He isn't perefect at all, he makes mistakes, etc. but he's been highly important to our build-up play since 2020, 2-3 months aside.