Since the OP mentioned rotating DMs, when does your turn come up? Seriously. If none of the other players/DMs will do anything about it, do it yourself. It sounds like the only think he does is basic attack, since alot of paladin stuff is only advantageous in close combat, and even if he did throw a dagger for a big daily power it'd do decent damage if it hit, so he must not be doing even that. Well, that's when you introduce his character to a lurker monster. Hit him with a creature that is honestly better at doing what he wants to do in the game and ensure that everybody else is busy with their own challenge and doesn't have time to bail him out. Defenders are good at what they do, but so are strikers. Use one that moves him around the battlefield, pulling him out of position to get momentary aid, and does great damage. If the lurker is an elite (which would make perfect sense if for some reason it was the boss or sub-boss of the adventure, and served a god that can't stand the Raven Queen, you don't have to work hard to explain the enemy trying to murder him so badly). He should win, but need help from everybody else after the fact. He should also see that if he were truly playing a character to the role he describes his character being, he'd have been better able to handle himself in that impromptu duel.
You could also introduce an NPC who is lawful good and honestly wants to help the party. Useful NPCs get a share of the XP automatically, whether the PCs give them treasure or not. And if the NPC is really good at being a defender, like any Fighter NPC should be, then the PCs won't kick him out of the group to save the Rogueadin's feelings. They will however start to resent that even though they are still getting the same amount of treasure, they are losing XP and someone in the group doesn't seem to be contributing. Despite good intentions most RPG players are still somewhat mercenary. If a DM introduces a crutch that is too good to give up, but it saps XP they will eventually figure out a way to equalize the XP equation. In this case, it should be, hey, we're sorry but we're gonna have to enforce the charter, because you just aren't as useful as 'Sven' and you cost us money too.