Fantastische Hure said:
Zamasu did know he can transform.
That's questionable. After all, Gotenks couldn't go SSJ in base until after the Rosat training and Zamasu had no experience dealing with transforming Potara fusions due to it being an ability reserved for Shin-jin. It's plausible he believed Vegetto couldn't transform, especially considering his reaction to seeing Vegetto do just that.
Besides why would they use SSJB, if they could settle for SSJ, after-all the fact that they were too powerful as SSJB could have crossed their mind?
As I've mentioned before, the necessity to give Zamasu no chance of using his immortality. Even if SSJ Vegetto could stomp him, there was no guarantee they could override his regeneration threshold, especially when the gap between Base Zamasu and SSG Goku wasn't enough to cut it. Hitting him with everything they had was Vegetto's best and only alternative. This is made very apparent by Vegetto Blue even saying he'd give Zamasu no time to regenerate.
Fantastische Hure said:
Maybe I agree. I thought some stuff through. Still though SSJB >>> SSJG is quite clear and I don't take the "less than 10%" statement as strictly as others do, if the story says it's less than 1% (later-on) then it is so to me. Not technically wrong, just Whis' wording would sound weird.
It still makes sense for him to be close to 10%, otherwise why wouldn't Whis say another relevant benchmark percentage such as 5% or 1% if that were the closer amount?