Well damn, I had no clue red essence did that. I thought it only unlocked your move set. Never played without it so I assumed that was just the default speed.
Yeah, I hope they change that, too. There were a lot of things that made me dislike IG in Wilds but that was one of the bigger ones.
I remember reading that bosses just scale to the amount of players so my guess is solo is actually solo. This would make the solo or trio only decision even stranger…