I think Goku went all out to deflect Boo's Kamehameha and it looked like if he definitely couldn't have tanked it. But he was confident in winning, even though in the living realm SSJ3 drains more energy. I imagine he had a similar edge to Boo as SSJ Goku or perhaps 100% Freeza would have to a...
He caught Zamasu in his telekinesis at one point and Zamasu had no monologue or anything indicating he thought Kibito was a lightweight, even assuming he was flattering him to be nice.