Pvp is not necessary to make a good extraction game.
Propper balance is.
The issue with arc raiders pve were many, the first being that there was no separation between pvp and pve, which just meant all the toxic pvp players went into pve to grief anyways.
Then as you said, people would wait there for keys because they'd farm items to take into pvp.
You have to seperate and properly balance pve.
There need to be less raiders per map in pve to make encounters feel more random, and stop 20 players being in matches all going for the same 5 key rooms.
There are a ton of ways to fix arcs pve problems, you just have to be a little creative.