If you have many versatile players, you don't actually need 2 players for every position, especially with the 5 subs rule ( not in spite of it!).
As Pep likes to say, Bernardo and Foden can play in 5 positions. Arguably, Alvarez can play at striker and both wings. Cancelo - at RB, LB and RW. Stones - CB and RB. Dias - RCB and LCB, Laporte - CB and LB (if we don't have other options there), same with Ake. Rodri, Phillips and Gundo can play at 6 and 8. Kevin - 8, 10, false 9.
Only 4-5 outfield players are narrow specialists: Walker, Mahrez and Haaland, to a lesser extent Grealish and Palmer, the latter two can play at false 9, Pep used them there in 1-2 games last season.
Given how many versatile players we have, Pep's idea to rely on 18 experienced players and 2-3 academy talents is probably justified. If we have more injuries than expected, we may buy players in January.
We need a new LB. But Pep might be wondering whether JWE deserves a chance. The problem is his injury record, not the talent.