Revan + Meetra + Scourge posed a legitimate challenge to novel Vitiate on a dark side nexus.
Is peak Revan - Revan reborn + Nihilus + Traya + Sion - Meetra - Scourge < Valkorion - novel Vitiate - dark side nexus?
I'd say it probably isn't. So the team has a chance, but given that novel Vitiate probably still would have won, I'm not sure how big of a chance it is.
In the actual fight Meetra could have killed him with a simple lightsaber throw, being a Jedi she opted to save Revan. Scourge's visions then fugg up completely, whereas previously he only recieved images of their mangled deaths. When the three stand together against him, they had a split chance according to his visions.
But his visions are hardly concrete, point is, in the actual fight Meetra could've cheap-shotted Valkorion, Outlander cheap-shotted him too.
Against a far stronger Revan, Darth Nihilus as Force back-up, Darth Traya as support and Darth Sion who can surprise him with immortality. Yeh Valk ain't winning.
Valk has five airborne lightsabers to deal with, plus the lightsabers on their person. I don't favor his chances here at all.