Dathomir would amp One sith as well, they lack the environmental advantage but Krayt is faste and Wyyrlok can provide support with spells/illusions.
Krayt and Wyyrlok win
__________________ "Happiness is a lie. Life is horror. The light is always dying all across the universe. The last star will flicker out someday, when it does, all that remains is shadow. And I will be its king!"'-Amahl Farouk
Well Talzin did go toe to toe with Sidious in the Lightning contest (even if she was Ultimately going to lose). But even that was on Dathomir so on her own personal nexus of power.
That being said, it should have been Talzin and Maul V Sidious. The front page of that comic really mis-sold that. Grievous was just annoying getting in the way there.
Palpatine didn't one-shot Vader. It was a 6 second-long burst of Lightning at maximum power (Sidious said "You will die", so he was trying to kill Vader), and the scene isn't canon anyways. Vader was captured by rebels in TFU 2, so the game takes precedence, because there is a contradiction and the game has a superior canonical level.
For the battle, team could take this, though Talzin should be more empowered by Dathomir than them. I'm undecided, however.