Brown was a very good puncher ,and a fair boxer ,but he would be too slow and predictable for Leonard who would comfortably outpoint him or force a late stoppage,imo.
Most of you are far more versed in boxers' overall histories than I am, so I offer this opinion with a good dose of humility. My dominant memory of Brown is watching a cagey veteran named "Bumblebee" Long challenge him for the title and seemingly give him a pretty slick boxing lesson for five or six rounds before gassing and suddenly coming apart like a cheap suit and getting stopped. I know Brown was a dominant fighter for six or seven years with a great record, but I have a hard time seeing him not get outslicked and left way behind against a master like Leonard who never had a history of breaking down under pressure. I do remember there was speculation in the magazines of the day that Leonard wasn't eager to test him, though, so maybe he knew something we don't?
Simon Brown is someone that I have always had a certain appreciation for. Brown is not an all time great, but he was an all time good. Brown would have been good in any era; a titlist in some, or at the top of contenders in others. Leonard's speed would just be too much for Brown. Brown had a decent punch, but Leonard survived Hearns and Hagler. If Leonard could deal with Hearns' punch at welter, and Hagler's punch at middle, he could deal with Brown's. I see Ray winning by decision, or late stoppage. It really depends on how hard Simon presses.
I still think he's rep as a puncher outweighs his ability. He's an excellent puncher for sure, but i fully agree with Mantequilla that Leonard is the better banger of the two.
Maybe, Brown could havescored a KD and given us some drama. Leonard's punching accuracy would be the difference here. Oh and the fact that he was just better. but teh Leonard who returned to the ring after the lay off might have got dropped for a quick count...