Woah, woah, woah there.
So you're saying, if someone dies, the game
gets easier to suit them until they stop dying? Haven't you considered that this might prevent the growth of the player? If things that challenge them are reduced in challenge when they fail, then what is the point of even playing?
The loss of the 2 XP bonuses are negligible for a non TR character, as there's a glut of it at most levels, and the repair bill is likewise negligible. They're a penalty for failure, if this penalty also comes along with a tremendous "boon" of the entire dungeon being nerfed to hell when you re-enter it, then it's a penalty that many would just take, to their detriment. They'd power through the easymode dungeon and expect that to be the norm, and never learn how to overcome what actually killed them in the first place...
It's in no way balanced - the penalty is exactly the same as what is in place now, and
the additional "gain" (and I use this word loosely, since in the long run it is not a gain at all) is very large.
To reiterate:
This is exactly what happens now. Except, now, the player is forced to reassess their strategy or improve their gear or supplies before jumping back in.
With your suggestion, they can jump back in blindly and do exactly what they did that got them killed the last time, except they'll succeed now because the dungeon made itself easier for them.
If you're having trouble with joining a premade GH group, then make your own, so that you are the starting melee in the group and are looking for casters/healers. Yes, it only increases the competition, but there is not much else to be done.