I think Cui would give 18k Vegeta a good fight. Vegeta would win but it seemed from a narrative standpoint that it'd be tough for sure. His win would come due to his skills and innate warrior ability, but it'd be tough. The story seems to prioritise similar BPs in face of skills. Vegeta could make it easier by using some tactic like sand in the eyes like he did bs Monster Zarbon. I think his battle vs Monster Zarbon can be one in which they were dead even but Vegeta's battlefield expertise allowed it to be quick. Though Vegeta counted on Zarbon coming at him off guard. Cui would know Vegeta would have the same power as him so he wouldn't come off guard. In the end, Vegeta's tenacity and more ground knowledge would give him the win, but he wouldn't go out unharmed. Imagine something like Goku vs Piccolo Junior in the 23rd Budokai, with the exception of the surprise mouth blast, in which Goku's wits outsmarted him like using his own blast against Piccolo, tricking Piccolo to be giant.
Tbh Vegeta has shown great durability during the battle on Earth. I think his battle vs Cui reflects better what a 1.33x gap is supposed to do.
Most judge Vegeta vs Recoome as 1.33x as well and that wasn't nearly as one sided as Vegeta vs Cui. There Vegeta's tenacity could come into play, but it's also possible Recoome was playing with Vegeta a lot. He let himself be attacked, he was laughing through most of the battle, even wonders "don't you have anything else? So I'll have to kill you". So Recoome seemed more like in a playing mentality. Or maybe he was like 36k. But idk, the blatant 1.33x gap confirmation we got which was Vegeta vs Cui ended up in like 3 blows.