Delph was makeshift, Zinchenko is on a different level. He is a top class and specialist (in Peps tactic) left back.
I don't disagree that someone like Gosens or something would be a good alternative to have especially when Pep will often switch between a LB that tucks in (Zinchenko) and an attacking RB (Cancelo) and then attacking LB (Cancelo) and RB that tucks in (Walker). Cancelo is not a bad LB but we do hurt his natural game playing him on the wrong side so Gosens or similar would allow us to have complete rotation on both sides at all times.
For how Pep wants to play in 95% games there aren't many more comfortable and suitable than Zinchenko and I have been very iffy with him for a while but eventually you just have to see what he is bringing.