As a test I tried to only do Play With Others missions and get through story missions that way. It worked fine but once I got to Ghost Town missions, after a couple of missions I didn't get a single mission in Canny Valley's Ghost Town areas in a week or so. I just couldn't for the life of me get my third visit to a spa because I never got thrown into ghost town missions. It's funny how broken PWO is.
I've been reading up on this because the challenge/trophy seems so ludicrous and it's actually not quite as bad as you'd initially think. You could grind it in "just" something like 24-48 hours. You just need a friend or two, gather materials and then mostly do missions that lower the price of a structure to 6 with constructors and everyone in the group goes crazy with building shit (not too much, though, apparently the game is prone to crashing with too many structures), since other people's building counts towards your numbers too. It used to be even easier when Constructors had perks that lowered the cost to 3 at best, but in true Epic fashion nerfing anything actually useful is the name of the game and they can't have you actually enjoying/making full use of the the building aspect but want to make it as tedious as possible.
Guardian Angel is worse because you can't really grind it much. A single mission generally only has 6 or 7 survivors. 15 or 16 in Rescue The Survivors missions but those are ultimately quite rare especially the further you get in the game and it's not necessarily all that common that you'd even find all survivors (either your team sucks and lets survivors die even when they go by them or you just don't have the time). Like, currently I only have one of those available in Canny Valley. If I don't want to go do missions in previous regions and get shit rewards/exp, I'd have to grind that one mission (and get less shitty but still shitty rewards)
