So I took a look and I believe the quote you're referring to is Goku saying "The only way to get stronger would be to merge with Vegeta, and even then I don't think I could win." It's from the end of episode 5. First of all, that statement is not at all definitive. However, judging from what happens in the arc itself, we can safely assume that the boost from SSG was bigger than potara fusion at that point in time.Doctor. wrote:It doesn't matter to which Vegetto it's referring. Goku basically says "The power boost of Super Saiyan God is bigger than the power boost of the Potara (with Super Saiyan on top)." We're not talking about character strength or powerlevels, we're talking about an established plot point: SSG's boost is bigger than Potara's.
I stress this point because fusion doesn't exactly follow conventional rules. You've talked about relative strengths in a couple posts, but I feel you're viewing fusion in the same vein as, say, going Super Saiyan. In other words, you're viewing it in the scope of linear progression. For anyone that hates math, you might want to stop here; this is simple stuff, but it's math nonetheless. Also, please do note that the exact numbers are not what's important here, but the concept.
Goku going from base form to SSJ is a linear increase in power in terms of numbers; if Goku is x, then SSJ Goku is 50x. In the same manner, Goku going SSG is also likely a linear rise in power. There's no "official multiplier" for it, but just for the sake of this, let's say SSG is equal to 5000x.
Fusion, however, is likely more of an exponential increase in power. For example, if Goku (x) fused with Vegeta (y), their power would be something like (x + y)^3. The rise in power is WAY more than a transformation; this is backed up numerous times in the Buu arc. This is important because it means that the increase in power is far greater the larger the variables (x and y) are. Kale and Caulifla are almost certainly stronger than Goku was back when he first fought Beerus in Battle of Gods. Ergo, their fusion is likely to be a far greater boost in power than if Goku and Vegeta fused back in Battle of Gods. Great enough to, perhaps, trump Goku's linear 5000x transformation.
Obviously none of this is concrete. There's no definitive answer on fusion. But it's food for thought.