The Superhero Database Classification number, or SHDB Class, is a number that represents the overall 'power' of a character. All traits of a character are used for calculating the Classification.
What it DOESN'T mean
This doesn't mean that a higher class would always beat a lower class character. But the bigger the difference in Class is, the more obvious it is who'll win in a fight.
How is this calculated
( INT^1.3 + (STR*0.5 )^2 + (SPE*0.5)^2 + DUR^1.6 + (POW + (SPS*SPL))^2 + COM^1.8 ) ^ TIER
Super Power Score and Level
Every Super Power has a score (SPS) that is used to calculate the Class. Each Super Power also has 3 levels (SPL). The level is set when connecting that Super Power to a character. The level determines the final score, of the Super Power, being used in the calculation.
The main reason Vegito wins is because the Potara fusion doesn't require Goku and Vegeta to have exactly equivalent power levels to fuse while the Fusion Dance does. That means that Vegito has an advantage over Gogeta in terms of power if Goku and Vegeta are not equal in power. While it's true that higher power levels don't guarantee victory, it still makes it more attainable for the stronger fighter. Therefore, Vegito is more likely to win because of the advantage in power.
Although it was stated by Toriyama himself that Vegito and Gogeta are equally matched trump cards, this has been proven false in the case of Goku and Vegeta having inequal power levels. I'm not dismissing what Toriyama said and will agree that his statement is true in a case where Goku and Vegeta's power levels are equivalent without either one lowering their power. But since a controversial fact is that Goku always has a higher power level than Vegeta, this means that Vegito still would constantly have that power advantage over Gogeta.
Dbs gogeta >>> dbs vegito
Sdbh gogeta >>> sdbh vegito