I actually think Buchanan would have fared better against the slower paced version of Duran that showed up in most of his subsequent title fights.especially in that period immediately after their fight where he was still learning his craft.
Ken wanted the rematch but Duran started the series with Esteban and that loss was big to a Puerto Rican vs Panama rivalry. Ken deserved a rematch and although I think Roberto would edge it, it was a tough fight,Ken was gritty. Ken went on to lose a disputed decision in a close fight(Harry Gibbs had him slightly ahead) to Guts Ishimatsu (for the title) a fighter that Duran had stopped. This fight should have been made, especially after the Duran/Buchan (low blow stop)
I believe that Duran was being truthful here, BTW...and not playing that game of "the guy I whipped was my toughest opponent" and not the guys who beat me. Buchanan WAS in fact the toughest guy Duran fought at Lightweight...no other guy at 135 could hand in there and take it like Buchanan did...and it wasn't as literally one sided as the scoring indicated. Buchanan would have made it to the final bell had he not been fouled, IMO.
Also i remember reading Buchanan was offered a rematch in Panama but declined it citing it had to be in Madison Square Garden as the contract called.
Buchanan has come out on more than one occasion wingeing about the fact that he didn't get a rematch. He's not the sort to duck an opponent, anyway. And I think he was a much better Lightweight than you (and people generally) give him credit for.