There's no proof that SS3 or SSG could evaporate him. The gaps between these forms are super huge and that's exacerbated by the fact that Gogeta is a fusion. Beerus literally left SS3 Goku dazed with a single flick of his finger, then there's Broly who could tank SSB Gogeta's attacks for days. If the gap between SS3 Goku and SSG Goku were 10,000x, then the gap between SS3 Gogeta and SSG Gogeta would be like 1,000,000x+. Assuming Beerus didn't unleash more of his strength against SSG Goku than he did against SS3 Goku, it's safe to assume Broly is much stronger than SS3 Gogeta.