Yeah the issue with the loot button idea is that there are 3 options: 2 chests, 1 chest, or 0 chest. I suspect it might be difficult to create an option for 1 chest groups within the PF system (I guess it would require the game to prevent further members with weekly clear from joining after the next person would remove the 1 chest). And it would make the system a bit complicated for groups that accept two or any of the three options. So all in all, the simplest solution would be keeping the current system while upon accepting to enter the duty the game would announce to all party members how many chests the group would be entitled to if they win.