Depends on the versions of Gatti and Broner. For instance I'd pick shot 2007 Gatti over current self destructing Broner.
Broner is one of the most hated boxers because of his unlikable personality, contrary to Gatti, but stylewise he's bad opponent for Arthuro. And let's be real, in his prime Gatti was beaten by Ivan Robinson twice, and Broner is way better than fringe contender Robinson.
Do you really think a fight between Gatti and Broner would look anything like either of Gatti's fights with Robinson?
No. Broner is better than Robinson and hits harder. But he's very annoying person, I understand why people dislike him
Pains me to say it, but probably Broner. Although if it got into any kind of war Gatti would kick his ass.
The point is, I don't think you can use the Gatti/Robinson bouts as a measuring stick for how a Gatti/Broner bout would go. I'd suggest that this also makes the comment on Broner's power, which is not out of this world, a little irrelevant.
I guess the best place to put this fight is at about 140 lbs. Gatti circa 2001-2003 (Ward, Gamache, Branco, Leija) v Broner circa 2012-2015 (DeMarco, Taylor, Rees, Malignaggi, Molina). Some of those were 135 fights but tbf both Broner and Gatti were huge drainers so they should be coming in the ring around the same size. Gatti with a slight height/reach advantage. I think it would be a great fight tbh, I think they could match up well, at first I was think Gatti would need to earn Broner respect otherwise he'd get ran through but who has Broner really ran through, he couldn't with Paulie, Granados, Taylor etc and the only guys he has have generally been coming in with a distinct size disadvantage like Litzau, Rees, Perez, Escobego etc. Gatti has form for being inconsistent too, loses to Robinson X2, Manfredy, Ward, I'll discount the fights against elite fighters as those were expected. Then against you can argue Broner lost to Ponce, Granados and Vargas on top of legit loses to Porter and Maidana. We know how Broner will fight as he never really reverts from his low tempo, one punch at a time attempt to shoulder roll tactics. Gatti has better footwork when he chooses to use them and a better shot selection but being Gatti he could also just revert to brawling. I'm gonna say Broner edges out a close decision with a knockdown or two swinging a close fight. Gatti starts the better outboxing Broner but stays gets caught and dropped then reverts to chasing Broner into an all out brawl thenceforth, winning rounds and having success but also getting countered, hurt and dropped enough for Broner to take a close fight. Similar to Broner v Granados but with a bit more drama over more rounds.
I see Broner methodically drilling Gatti with hard punches out of his Philly shell all night. Broner wide UD or late stoppage.
I can't see a guy, who got pushed close by an aging Mallignaggi and allowed himself to be overpowered by Maidana, really making that much of an overall impression on Gatti.