Yeah, this.
It is well estabilished that Fusion is hax.
Super Buu was stronger than Goku and Vegeta together. Stomped by Vegito even even he had Gohan's power.
Janemba was far above them as well, but completely hopeless against Gogeta.
Omega...lol.
Unless the power boost for SSGSS Fusion is significantly smaller than the usual, Beerus stands no chance.
As for Whis, impossible to say.