Had to Google Sion, he's not part of the books, I don't really know him yet.
Zannah was... Dunno. I'm still ambivalent. Eventually she fought Darth Bane at the peak of his power, but before that she tried to take him on in the Doan underground while he had just escaped torture and was missing his lightsaber. That felt pretty wrong, especially because we were told throughout the books that she 100% accepted Bane's philosophy, and that didn't really seem in line with that imho.
Hoth felt like a small C'baoth although probably C'baoth would have walked into the cave convinced he could stop and survive the bomb.