I agree, having to rely on other people, this absolute nonsense in a massively multiplayer game XD

Irony aside, when players did suddenly quit my team when reaching high floors, it was each time after getting the black pegasus mount. They were after that from the start, and not completing the whole dungeon. Of course, they didn't say anything of it beforehand. Allowing matched parties will not get rid of this kind of people.

As for making a solo friendly version, that would only cause another forum huge uproar where the community will bash SE for making fun of players that already did solo it the hard way. Or would need to have different loot, achievements and rankings than the normal version, but then you would still feeling frustrated to not have completed the real thing.

In the end, your best bet is still to try to find really reliable players, with some of the hints who were given to you.