Garcia (I’d prefer THB but it obviouslt won’t happen under Pep) with Otamendi and Fernandinho protecting them would be far more solid, or even a back 3 of Walker, Garcia/Rodri sweeper and Otamendi.
The capacity to tactically foul is what defines Fernandinho - the difference between him being a good player, and the great one of the past few seasons. In defence, when he’s the last man, you neutralise that element of his game to the detriment of the team.
Rodri, for all of his quality on the ball, is a massive downgrade in that regard, so with him being seen as the long term anchor, the defence is going to have to be upgraded - leftback especially - because they’re going to have do a lot more work without Fernandinho making them look competent.