Both
I have finished DOS2 in single-player and multiplayer of 4 players and I actually had more fun in my co-op experience than the single-player experience and the main reason for the enjoyment was the group I have played with are more into single-player games than multiplayer so when we decided to try DOS2 we wanted the game to still feel like a single-player game but instead of Loshe, Ifan...etc in my party now I have my group to control any one of them or play with a custom character.
it actually might be one of the best gaming experiences I have ever had because of the multiplayer aspect.
and I think one big aspect where it is clear that the game is designed with taking into consideration the co-op aspect is the map design.
I can see why people complain about BG3 theme park map but recently I have started playing WL3 in co-op (I have played it alone before) with one of my friends since it is a 2-players co-op and my god the loading time and how frequent it happens during the game might kill us since it is clear that the game is designed for the single player but we still want to play it because it is really a good game
but for everything we have to do we have to go through a loading time and stare at the screen for at least 20 seconds!
not just that but the fact that I have to be on the same map as my partner to do anything.
Like, I remember one thing that annoyed me so much while I was playing WL3:
we were at Downtown Colorado Springs and I was doing a quest when my friend wanted to respec his character.
I was like ok go for it but he had to go to Ranger HQ which is literally a place next to Downtown Colorado Springs
but there is a loading time between these two locations.
So I had to go with him to respec his character and then go back to do the quest (two loading times for that).
that was really annoying
and there are more examples but this might give an idea of how bad the map design is for the co-op experience
