but JBJ doesnt have the accuracy or the power that silva has
however with silva coming into this fight as the MW version of himself and not the more powerful LHW version, i suspect it might take more than one round for him to finish bonnar
He doesn't need more mass to deliver enough damage to drop LHWs or even HWs as he doesn't use brute force to KO people but accurate technique. He's one of the few people who actually are able to apply the martial arts concept of using your opponent's force against him. That way he dropped some of his opponents with minimal force of his own (jab knock downs on Griffin and Okami). Bonnar's wild forward walking style is taylor made for Silva's counter where he just needs to stretch out his fist and let Bonnar's forward momentum do the rest in the power equation. It's like making him running with closed eyes face first into a brick wall.
He'd only need more mass if he were afraid to be pushed around by physical stronger guys and to be able to absorb more damage on the body, but concerning delivering damage, his MW weight is fine enough.
I wouldn't be surprised of a 1st rd KO.