After learning that writing a custom script was currently the only way to sift, sort, and filter users by more than one field; and after deciding that I am not up for that right now, I dove back in to slog through my user list for pruning. To my pleasant surprise I found that when I sorted the list by POSTCOUNT it was also sorted by JOINED, automatically! Either a NodeBB angel updated the user list sort functions or I am just seeing life from a different perspective. Yay! Pruning done in no time.