Super characters are overrated for the sake of it.
We know that SSG Goku in Battle of Gods is stronger than SSJ Vegito but that's about it. We saw an Enraged SSJ2 Vegeta resist Beerus for a little while and power scaling logic would suggest he was still infinitely weaker than SSJ Vegito.
Base GT Goku is scaled around SSJ3 Goku level going off his fight with Rildo and SSJ4 Goku has a calculated x4000 multiplier (compared to Adult Base, let alone kid version) and he's much stronger than Z SSJ Vegito, also considering how Goku stated Baby Vegeta was the strongest he ever faced. And he gets even stronger over time, expecially during the fight against Syn Shenron, when he surpasses his SSJ4 limit.
BoG happened some months after the Buu Saga but that's no big difference. GT happened over 15 years later.
Even a low-ball estimate would place SSJ4 Gogeta above an hypothetical SSG Gogeta from the Tournament of Power, who would comfortably stand above Kefla and by a huge margin.