Is anyone else attempting to beat all missions in this mode? I managed to slog through the first planet and am currently stuck on the infamous "command center" (base building escort) mission on the second planet

The insane difficulty makes some missions impossible, yes. It just doubles all the enemy spawns and the game was never tested for that. I got quite far on impossible, but some of the escort/protect missions are not beatable with the double enemies. The enemies just overwhelm the protection target no matter what and there is now way you can kill them all in time.