hoegenaamd I agree with you that D2 is not party-friendly, but D2 is the only end-game field map in the game right now. Even with recent updates to kRO, it still holds the throne as the place most people aim to farm. And crowns should be pricey since they are BiS and will remain BiS even after recent updates to the game.
Progress should be smooth, and we already have a huge margin of accessibility to the content with the fact that crowns are not account-bound and TD weapons are really cheap right now. So, it's not uncommon to see people skipping Illusion > TD, which is far worse for the middle part of the economy than the end-game map being farmed by, well, mostly end-game players. Also, with the release of HoL, that map will lose a lot of its might once players catch up with the gears, and even though later parts of HoL need you to be end-game in order to progress, earlier stages can be done with mid-game setups. So we'll have a more clear interaction between HoL/CT > D2 > HoL/CT > D2.
I don't see party play changing there without an overall change to the whole looting system since the problem is that, in the end, you will be contesting with fellow party members for low rolls, and the quest numbers are quite high for slower parties.