Would Sean O'Malley (Or any other elite Bantamweight) be able to win a fight against an untrained 220 pound 6'6 bodybuilder?

Size can be factor. Yet with a rained small guy. Smaller guys rely on technique and skill.

Personally i am 1 of the smaller guys. And when going against a big guy, like in your scenario, there are things i can do to a smaller person  know I can not apply to a larger person.

So training does play big part in any situation and knowing how to/not to apply that training is even a bigger part of survivability.

Not many get out of a fight without getting hit a few times. You have to take what you dish out. Hopefully you dish out more than they can take

Lmbo. Bodybuilders are weak most of the time...

A really big bodybuilder like that likely has a strong neck too and hasn’t taken a lot of shots. Might be able to absorb shots from a smaller guy pretty well. That said, I would bet on O’Malley if the big guy is untrained. O’Malley is local to me. He trains at the Lab under John Crouch, a legit black belt under Royce Gracie. I think he could find a way to get a submission. Not a 100% guarantee, of course.

Size is definitely a factor, and at its extremes can make up for a lack of skill. But I don't think BW to small HW is enough of a disparity. Especially with someone untrained. Sean is a pretty tall BW at 5'10. He probably walks around at 155-160. Not sure how strong he really is. But I do know a lot of the elite MMA gyms intentionally have people train with people of varying sizes for experiences. There are lots of stories of people getting the job done with weight disparities. The Thais in particular are known for this in the earlier combat sports days.