You can't have maxed toons and only 20k power. I'm sorry, all due respect to your arguments, but the accepted parlance on these forums is that "maxed" currently means 7*, g11, regardless of level.
Anyway, to address your original question, do the older PvE events even use the new/reworked toons? I will check this challenge specifically later, but I seem to remember playing a PvE event with a Boba boss after his rework and it was the old version. Also, there are RGs that don't taunt, and TFPs that don't throw down AoE buff immunity. Also, even in the new Krennic events, Boba didn't gain his buff until after he killed someone, and Jyn didn't seem to revive.
So I don't know that these challenges are affected by the rework. Again, I'll try to check, but encounter five on these things is typically much harder than the other four. 20k power is nothing. Health challenge is way easier than the others so it doesn't matter if you used three of the same toons.
