The burst of clarity showing Tython beating Vitiate does not necessarily mean Revan and his team cannot. Yes he saw them defeated, for, showing that if it was a burst of clarity, it would have been the canonical fate according to you, so he could have ultimately been seeing himself betraying Revan. If his vision showed Vitiate striking down Revan, it could have all we known been like the novel, and Revan is distracted by Scourge killing Meetra. We will never know.