Ok this is the important bit to me.
This isn't about a lame duck character at all, it's about a player who wants to game with a group but doesn't like the system and game that's currently being run. Which is a far bigger problem and not one I think is resolved in any way from "within the game".
If he was just playing an underpowered character and having fun without trying deliberately to disrupt the game then I would try and suggest ways of fitting it it.
By the sounds of it he doesn't actually want to be playing the game, he wants the group to be playing another game. And unless the group decides likewise, he is basically stuck.
There can be a certain rebellious stage where a player declares "D&D isn't proper roleplaying! I hate classes and I hate levels and I want point buy, it's SOOOO MUCH BETTER FOR CHARACTERS!" At which point they sometimes run away and get it out of their system, then realize D&D is actually pretty fun when you buy into it.
(I vaguely agree that D&D isn't a good system for trying to run anything other than D&D, likewise I am also sceptical about just how generic many generic and "universal" roleplay systems actually are.)
I think at this point, you kinda just have to ask them they do want to stay in the group and play D&D or if they want to move on if everyone is happy with D&D.
Point out that you're aware he wants the group to be playing something different, but D&D is the game that others want to play.
Awkward if you're the only roleplay group he can play in since he has a choice.
Sadly I can't see a solution beyond him coming to this realization himself.
Just stop carrying him. He keeps doing this because your group is "nice" and carries him, you heal him, you protect him, you try to teach him the right way to do things and he is refusing to change. The simplest solution, if you wish to keep playing with him, is to stop enabling him. When he drops to 1 HP, don't heal him. Force him to choose to retreat or defend himself. When he drops to the ground, make him the last priority. When he charges into the fight, don't cover for him, let him do it.
I notice that you mention later that he doesn't like D&D. Not liking D&D combined with this playstyle makes me agree with CCS.
Let me be blunt: this guy is not your friend. This guy is a selfish jerk who knows he has power over your table (because he hosts). He doesn't want to play what you all want to play and he's doing his best to make it as un-fun as possible. Carrying him as made him the center of attention and he likes this because he's getting what he wants: everyone to put up with him while having no fun at all.
You should prioritize relocating. Take away his power. Then evaluate his friendship. You may find the latter of lesser value when you're not worrying about him having a fit and throwing the group out.
I've had my problems with powergamers and other editions, but I don't take them out on every player and every edition of the game. This guy thinks that is OK. It is not.
A lot has happened since I posted. I realized that I was just not interested in playing with all this drama anymore so I took a break from the game and maybe the group. Since 2005 I have been the one that has been called on to fix every problem and deal with hurt feelings, tantrums what ever. I turned 58 in December and I am just sick of it.
There is the big myth in all the books I have read on DMing that a good DMing can handle all the different play styles at his table and make the game fun for everyone but there is an important caveat to this the DM can only do this if the players all cooperate and compromise so everyone has fun at the table.
Most of the players who make up my group, not all play in every game, are real life friends. The player in this situation is a great guy he is the type you can call at 2 AM in the morning because you car broke and he will haul his butt out regardless of having to be at work in a few hours to come help. But I firmly believe in this situation he is being a jerk and I am sick of it. I get it you hate DnD but you are choosing to play so either play and treat the rest of the group right or sit it out.
I started out playing basically old school with little role playing mostly kicking butts then came a long period of deep role playing and character building and while I do love it I am feeling a little burned out.