Kidd, his only contribution was creating a cage for Zeus and lift Big Mom in the air, but we know that Law could have just teleported Zeus out of the way.
Other than that, he didn't damage anybody, talk too much, distracting the other fighters. Very sad performance, he is lucky that Oda likes him a lot and forced his undeserved presence on the rooftop.
No he couldn't have. Zeus and Prometheus would have just returned to BM if they were teleported away. Which is why they needed a method of keeping Prometheus and Zeus away from BM.
For Prometheus, Zoro was slicing him via his flamerend technique. For Zeus, it was the cage Kid created.
Fundamentally, Kid was a major reason why they were able to separate Kaido from Big Mom and they likely would have been unable to do so without his help.
At the time Luffy was KO'd and Zoro had just taken heavy damage, so the only people who could have really done something was Kid, Killer, and Law.
Kid played a crucial role, not only in trapping Zeus, but also in repelling BM into the sky so Law could knock her off the roof via tact. This was a unique role that only Kid could have played, as NONE of the other members of the roof had powers that could have done this. Zoro can only slash, not repel. Law has tact, but tact doesn't have the raw force that magnetism has. Hence, Kid was the only one who could have knocked BM into the sky and given Law the opening to knock her out.
