I wanted to complete the campaign of the original Doom games with my friend, and I wanted us to have a pretty authentic experience of the classic games, so I said to go with Crispy Doom. The items spawned on a map change when you play multiplayer, which changes the campaign quite a lot (e.g. there's a rocket launcher that's pretty easy to get in e1m1). Zdoom has an option to turn off multiplayer weapons (although it was a bit difficult to find) but I'd much prefer to play Crispy Doom.

So my suggestion is to add an option for turning off multiplayer weapons in co-op mode.