I'm glad you raised this point. Last season Pep became notorious for not making substitutions & rinsing out our meagre best 14 in most games when fit & available.
Could this be because Pep had a lack of faith in Sterling, Jesus, Zinchenko, Aké, Gundog, Fernandinho & the EDS on the bench for not being good enough to make a significant uplift to our best 11, & we'd stand more chance of turning a defeat into a draw, or a draw into victory sticking with the main players Pep trusted most, even if they were in need of a rest?
It's not to say the players listed aren't capable, but toward the end of last season, none of them would have made our strongest 11, & all would've left in the summer if the Chavs had met our Aké valuation & reported interest in Gundog was more concrete.
However I believe both Gundog & Aké have played themselves firmly into Pep's main plan for this season & I'm happy both are still here.