He also seems to do some Arena matches! That was what I noticed and why I was asking
@scott: I think it was good old Sparton who explained the ironite and SoT drops very early and as far as I remember the general thing was that every enemy that is killed has the chance to drop 1 SoT/Ironite. From that we can conclude that levels with many enemies have better chances to give some drops. But of course I don't know if this still holds true, but I don't see a good reason to change that. This makes Powerslave even better as getting 8/12 and more SoT by drops is more likely than getting 10/15 etc. needed for the higher worlds.
Your other ideas are also very good so that the benefit of a specific level is made up by different aspects. Does NC madness always give 4* Talis, or how was that? But for sure these levels are too hard to bring 2 non-sharded Allies. This is not the case for NotB! It takes longer but basically Alex can do it on his own so you can level up some chars alongside. I did this during the event when we could buy XP+ for gold counting towards the "spend 5M Gold" event challenge. But as the Dungeons give a lot of 3* evo shards, I think I will go back to Powerslave farming - especially for using the troopers! Maybe some NC farming in addition but I need to test that.