5. Losing to one-shottable fodder, as demonstrated when Lord Scourge saw numerous visions about the outcome of his and his allies’ battle against Vitiate. In some, they lost and in others they won, but most importantly, Scourge was not able to determine which outcome was the most likely to happen, meaning there was a roughly equal chance of Vitiate winning or losing:
For Scourge, the universe suddenly seemed frozen in place, as if time itself had stopped. He realized he was at a crux in history. Fate and destiny would forever be altered in the next few moments.
The Force washed over him like a wave, and a million different possible futures flickered through his mind simultaneously. In some, the Emperor was no more. In others, he had transformed the entire galaxy into an empty wasteland. He saw both Revan’s triumph and defeat in the throne room. He saw variations of his own life and death, played out over and over in every concievable way, shape and form.
He had to choose, but there was no way to know which was the most likely outcome, or what actions of his would lead to which results. Revan had said visions could guide a Jedi, but for Scourge they brought nothing but confusion.
-The Old Republic: Revan
This completely invalidates your claims about Vitiate winning 10/10 against Tenebrous, when he can only win 5/10 against three people each of which he can one-shot with the Force. And Vitiate sure as hell isn’t one-shotting Tenebrous, who can casually block lightsaber blows without even needing hand gestures:
She was less than a meter away, her blade already slashing in for the killing blow, when she felt all the hair on the back of her neck rise. A shimmering purple cocoon of dark side energy enveloped Bane, a fragile shell holding back a storm of pure power.
She tried to pull back but it was too late. As her blade bit into the cocoon the energy was released in a sudden burst that sent both of them flying backward. Bane slammed hard into the wall against his back and crumpled to the ground. Zannah was tossed ten meters farther, landing hard on the stone floor.
-Darth Bane: Dynasty of Evil
Vitiate’s attacks aren’t even close to being as potent as a lightsaber blade, so Tenebrous will have no difficulty blocking them, either.
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In the end, no amount of godlike power and hype is going to help Vitiate when it comes down to personal combat, where he simply sucks. He has possibly the most pathetic showings in the entire mythos, relative to his hype he receives and his power level.
He has absolutely no way of putting Tenebrous down, when the latter can just deflect his attacks with a lightsaber or with the Force, or he can dodge them with no difficulty whatsoever. Tenebrous in turn can close the distance very quickly and chop him up into a million little pieces, but I doubt he’ll even have to, since Vitiate will probably walk into his lightsaber again, lmao. Or he can create illusions and phantoms to confuse Vitiate and easily kill him while he’s distracted. Or straight up overpower him in a Force battle.
Anyway, point being, Vitiate has no way to win, while Tenebrous has a dozen ways to win. It’s not a contest, Vitiate is outclassed here.