There are only a few warriors who can defeat Jiren as of the moment. Unfortunately, Hit was eliminated the moment he faced Jiren. Goku was out of commission because he is still resting from the lost of stamina. Vegeta might be able to stall him a bit, hmm. Even Frieza is afraid to fight against Jiren. And Gohan? Can we doubt on the idea that Gohan is getting a new transformation?
If we can’t really rely on unfused characters, the only thing that we can do is hope that a miracle will happen. Or, we can hope for a fusion to be made. The best candidate right now? Of course, it would be our playful warrior, Vegito. There is only one problem about this though, Potara Fusion is not allowed, and so as for fusion characters like Vegito.
But how well would Vegito fight against Jiren if he gets the chance? There is only one benchmark that we can do to determine Vegito’s strength against Jiren. Is Fused Zamasu stronger than Jiren? If yes? Vegito will destroy Jiren. If no? Then you know what’s the answer. Fused Zamasu was Vegito Blue’s latest opponent and he is the closest God-like warrior that Vegito fought.
But this is more complicated than power levels and transformations. Goku was actually able to fight teeth against teeth alone with his ultra-instinct form. So when we mixed in Vegeta and do some math, Vegito should crush Jiren because of his overwhelming power. But that’s not really the case in the whole DB series.
The thing is, Vegito, with all his might, will only be limited to Super Saiyan Blue. Ultra-instinct is a state where the body moves on its own without the brain instructing it. The case with Vegito is that he is a being from two different people with two different characteristics. Potara fusion is the fusion that combines two people to create one new being. A + B = C, not A + B = AB, if you do the math. Goku can reach Ultra Instinct, which is not achievable at the moment for Vegeta. The chance that Vegito will have UI will be 50%.
Sure, Vegito got high power levels and he is actually stronger than Beerus. But that is also a weakness because the fusion will be undone in a shorter time just like in the DBS manga. I do think that if Vegito will go all-out against Jiren early, he will get a high chance of beating the Pride Trooper. But when he uses more power, the more his time will run out. Because of this, it is not really a good idea to make Vegito battle Jiren in the Tournament of Power.