Permadeath which doesn't wipe your save is not significantly different than a game over screen. The typical player would just reload their last save. There's nothing impactful about that.
Permadeath isn't the way to make your choices meaningful. Quests with varied and continuing outcomes do, limited points available and no or costly respecs make choices meaningful.
D:OS has you with two players because of the story, so it's not just because of co-op that there is no permadeath. Oh, and there's no need to actually try it to see if permadeath would make co-op less enjoyable, because the answer is YES in 72-point font.
I think you should give my opinions the proper respect by marking your statements here as clearly your own opinions and not as they were a fact or something (I got at least the feeling while reading it...)
I told you about my own experiences with various party RPG games and I told you how about I felt in them. You cannot just wipe that away with a bland "the typical gamer would just reload". Maybe most people would do but at least you have the choice...
And I was talking about the impact of combat choices and not the impact of dialogue choices. These are two different issues or better two different layers of choice and agency. Permadeath was just one example of mine how to make combat more impactful. It's not an equation like "perma-death = better combat", not at all. All systems and mechanics have to work together to make the combat system impactful and worthwile.
Of course leveling and the danger of putting points in the "wrong" abilites or stats is again another layer of choice or meaningfulness. There is no indication that all these systems can't work together...
And I disagree on your statement that D:OS has two main players because of the story. I think that this decision was made after someone at Larian got the idea of a co-op game like we can see it now. There is no point in making a game about two characters for singleplayer, especially not in this case, as the game evolved to a real party RPG. And I think that if Larian is really honest about that they would agree with me here...
