Considering Smith is fighting this Sunday, I think back on his best win, Hopkins. For some odd reason, I believe that Smith would still win this match up, no matter how old Hopkins was. I think Smith's jab is all wrong from Hopkins.
The guy was practically a fossil man, and even then he was well ahead before getting knocked out late. A prime Hopkins wins a decision
Joe Smith has the advantage in KO power, telegraphs his punches, suspect defense and zero inside game. Prime BHOP will school him for at least 10 rounds on the way to a UD.
Hopkins of course. Even the version that got knocked out of the ring was fighting on even terms up until he got nailed. Smith isn't the best boxer out there. Though as nails and a huge punch, but not much on the technical level. His fights Barrera and Bivol told you all you need to know. And be fair here, Smith didn't beat Vlasov last year either, that was a gift.