–Zamasu speeches then powers up into growing really big and the scene cuts away. Fights come back later.
-Vegeto explicitly calls out that Zamasu can’t keep up with his speed now that he bulked up (something that people should recall from the Cell saga). This allows him to push Zamasu around a bunch, though he deals no visible damage.
-Final Kamehameha, Vegeto puts a ton of his energy into it (indeed, this is directly noted to be why Goku and Vegeta can’t go SSB later; it totally drained them).
–Zamasu emerges from the smoke, having seemingly not even been knocked down by the blast, and starts talking about how he’s a true god while spreading his arms dramatically.
–Vegeto teleports to the posing, defenseless Zamasu, punches him and defuses, Zamasu immediately recovers and one-shots Goku and Vegeta.
Prior to Zamasu slowing himself down, Vegeto lands exactly one hit during times where Zamasu isn't speeching, and he's the one who has to back away despite having Zamasu in a hold. Otherwise he consistently avoids getting into power comparisons with Zamasu, and gets overpowered when they do clash.
Meanwhile Zamasu repeatedly lets his guard down by speeching or slowly walking toward Vegeto when he seems to have the advantage. Prior to him screwing himself with his pseudo Grade 3 form, these occasions are the ONLY ones where Vegeto actually manages to hit him. despite being completely off guard these blows don't actually do that much damage.