IMO rewards to supportive actions shouldn't be locked to parties, more like giving decent reward on their own, regardless if it party or not. Its weird artificial limitation to make this party-based IMO. As for threads, uh, well, it also partially about "party" aspect and its use. That's why I posted it here. I dont readily understand how to put this consideration about "party" aspect into mentioned thread, would be outside of context due to relation to "party" as well. If someone undertands how to perform this better, feel free to edit or move my message the way you see it fits the bill.
Just removing level diff could be its own can of worms: how it would interact vs e.g. noob players, etc at big lvl difference? Newbies need very few XP to level up and I'd say they already level very fast. Even faster? Just imagine noob joining heavy lifters party on purpose. In principle XP share could scale or something based on level diff but it assumes someone have to code it.