I see, well having a good chin does not always correspond with being big and vice versa. I don't know how Brian Shaw would get on but he appears to be extremely sturdy and thick necked.
I am quite tired of bodybuilding contests and love boxing training and don't really know if I would have a love for real bouts unless I tried it like you say.
I think your example of a light guy wobbling a big dude is an anomaly, they have weight classes for a reason. But I,m not daft enough to think power comes from size alone.
Back in 2015 I think, I sparred as part of training a former heavyweight local boxer. He also happened to be a farmer who stopped me one day because I crossed his fence picking magic mushrooms. At the time I was more the stereotypical bodybuilder build but still had power. He threw a right that landed smack on that was not sparring level, nah. I stopped for a moment and smiled, it stunned a bit but nothing bad. I went out for revenge and got through with a stiff power jab but if it was today and he was still a younger man I would say let's rumble.
My last street fight was when I was 15 I think. It was around this time of the year and I was on a date with a lass from school. I was fit and strong back then already. A group of teens on the city walls throwing snowballs at people down below said "if you throw that snowball at us we'll batter ye" so I went and threw it at them, perhaps to impress the girl. I walked up to them and the "strongest" guy steps forward and we begin. I took a few but was nailing him hard and fast down the pipe. He stepped back and I lowered my hands inviting the group to take pot shots so a few others took digs but I stood there motionless then they ran off (true story).
Ps: still might have a hot bird tan my glutes next year.