Co-Op Dungeons (for DoW/DoM and DoL)

[Nakiamiie]

You don't need it.

I know that, but as an archer with only Defender and Rampart, it is rather difficult. The point is, the safe spots makes the rest of the fight easier (which is a good a thing from a casual point of view).

Of course that would happen to in a mixed dungeon. Almost impossible synthesis that most people fail (Hellfire) and puzzle parts solved before even entering the dungeon (safe spots). It will happen no matter type of dungeon.

Still, I don't see it as a valid reason to dismiss mixed (or DoH/L) dungeons.

I understand it would not be the cup of tea of everyone, just like many other features.
But the reasons Yoshi-P stated are not really problems, it only seems like they haven't fully explored the question yet (proof of that is that he speaks as if people were stuck with a single class, it's not the case. Even players with main class as DoL or DoH also have battle classes).
I believe it is worth exploring the idea and finding the proper combination that will make it a new type of challenge.