Having thought about it a bit, I could see it making sense, that hypothetical Gogeta could have a proportionally bigger gap on Gotenks, than Goku and Vegeta have on Goten and Trunks in equivalent forms.
As far as we know Goten and Trunks individually only have Super Saiyan, whereas Goku and Vegeta both individually surpass that and Goku can even go SS3, and I think it could make sense, that could be very relevant, when using Fusion, even when using a consistent Fusion multiplier:
SS Goten/Trunks: 5
25.
SS Gotenks: 250
400
-SS2: 600.
-SS3: 1,250.
SS Goku/Vegeta: 50
-SS2: 100.
SS3 Goku: 400
SS Gogeta: 800.
SS2 Gogeta: 5,000.
SS3 Gogeta: 5,400.
So here the Fusion multiplier is 50x, but it applies to their max power, rather than individually boosting each and every Super Saiyan form by 50x ie. in Gotenks' case, pre-RoSaT his SS form is 50x as strong as Goten or Trunks' SS form, but post-RoSAT SS Gotenks is "only" 16x stronger than SS Goten or Trunks and now it's his SS3 form that's 50x stronger than Goten and Trunks' SS forms.
In Gogeta's case, not only are Goku and Vegeta twice as strong as their sons in equivalent forms, but they also have further forms, in Vegeta's case making him 4 times stronger than the kids, while Goku is 16 times stronger, than them, thus that could be reflected like this.
Since both can go SS2, they get that multiplied by 50 and SS2 Gogeta ends up being far more than 2x SS2 Gotenks(over 6 times stronger), unlike the gap presiding between SS Gogeta and SS Gotenks. However Goku also has SS3. We can't tell how Fusion is supposed to operate, when one of the fuseés have such a large power in reserve, so I just added Goku's SS3 power to Gogeta as a reserve power. I doubt it's going to be multiplied by 4 like it is in Goku's case.
Anyways hope it wasn't too long, but that's just one of the ideas, I have on this subject.
