I just recently returned to the game, but years ago I’d run excavations or survival with unranked Warframes and equipment for faster affinity for mastery rank. Affinity booster helps even more. Oh, and taking along an OP friend for when the enemy levels get higher.
there was also a stage my brother and I used to run. We’d climb this certain part of the wall and could stand on this very thin ledge and gun down infested without being hurt. It would get to the point where we forced to quit (do to barely causing no damage because enemy level increased very high or we’d got exhausted- can’t remember exactly which). But that was years ago.