Fusion Multiplier is 1,040,000 times the base form of one user if two fusees' are equal.
Super Saiyan God Goku is supposed to be stronger than Goku and Vegeta fused as Super Saiyan 3.
Super Saiyan God = 40,000,000,000x
Super Saiyan Blue = 200,000,000,000x
Super Saiyan Blue Kaioken x 20 Goku = 4,000,000,000,000
Super Saiyan Blue Evolved Vegeta = 6,250,000,000,000
Dragon Ball Super Broly Wrathful State = 165,000,000,000
Super Saiyan Broly = 20,625,000,000,000
Legendary Super Saiyan Broly = 495,000,000,000,000
Mastered Super Saiyan Gogeta = 520,000,000 (He was able to compete with Super Saiyan Broly, which doesn't make any sense.)
I have Goku's Base Form in the Majin Buu Saga = 8,400,000,000. To get Gotenks to equal 8 times stronger than Goku, Trunks and Goten have to each have a power level of 64,500 in base form which seems a little weak.
Also if Super Saiyan Gogeta equaled Super Saiyan Broly than Super Saiyan God would have to be an only 998,400 multiplier. And most people know Super Saiyan is more than a 50 times multiplier, because Goku didn't go Kaioken x 20 on top of Blue and Vegeta didn't Go SS Evolved Blue. They knew broly was stronger than than full power added together. Super Saiyan God would only be 24.96 times stronger than a Super Saiyan 3, and if Super Saiyan God was 40,000,000,000 multiplier than a base fusion would have to equal 41,250,000,000 multiplier which seems way to high.
Lastly Ultra Instinct Goku being stronger than Goku and Vegeta fused as Super Saiyan Blue makes no sense.
If Jiren is equal to Ultra Instinct Sign Goku than Jiren using 1% of his full power would be literally over a million times stronger than an SS Evolved Blue Vegeta in the tourneament of power. Base Form Cunber being stronger than Super Saiyan Blue Kaioken x 1 Vegito is ridiculous. I believe that had Goku and Vegeta Fused into Super Saiyan Blue Kaioken x 20 Gogeta at the start of the tournament of power they would have beaten Jiren Easily. They didn't fuse in the tournament of power for two reasons, pride on both their parts, and I think they both thought fusion would be against the rules.
We all tend to forget one small thing that happened during Goku and Beerus's battle in the first saga. Goku's SSG time wore off but still, as a SSJ he was like a SSG(for only a little amount of time of course). He absorbed SSG's power and now in his base forms he is a bit more powerful than he was before. I believe also Cumber did the same. He lives on with his Legendary SSJ form that was once unlocked and absorbed it, which means he also mastered it, so now Cumber uses new forms, better that Legendary SSJ, unlocking his full potential and having it mastered. Also another thing we tend to forget is that Cumber has a tail, which means many things.
I would love to see a fully powered super saiyan 4 Cunber against an evolved blue kaioken x 20 gogeta or vegito. I think if Vegeta and Goku train to their limits in their natural states, then each of them individually with ssj blue kaioken x 20 will be stronger than a base Cunber.