I think it's Oscar's inconsistency from switching trainers that makes it hard for people to have an open and shut case in this conversation. He switched trainers so much he never really got settled. He and a trainer never really got the chance to gel and see what could be done in the long run. I think that screwed Oscar worse than him running at legit peaking A+ level talent when they were at their best. Floyd was consistent, so there's always that, and Floyd always came on strong later in the fight. He's not a sprinter, he's a long distance kind of guy.
If we take Oscar at his physical and most ferocious - dialed in, I'd go to the 98-99 version - not the one that reeled it in against Trinidad. JCC and Quartey wins. Although those weren't his best wins, though they were good ones, he just looked savage and sharp. I think if that version got in the ring with the Floyd from their 2007 fight, he might pick up more of the earlier and middle rounds. Remember, you only need 7 to win a 12 round fight. While Floyd usually picks up more rounds than he loses in the last third of the fight, ODLH might get going and make Floyd have to fight out of a real deficit. That version of Oscar I am drawing your attention to was a destroyer with his jab, too.
So, going back, Floyd is a more reliable pick because of his consistency, but if we are talking the best version of Oscar, turning up for one night, we have a real problem for Floyd. We usually see the best version of Floyd, so that is a constant. His dedication is admirable. But Oscar, while brimming with talent, just couldn't regulate and maintain.
I totally see the arguments in Mayweather's favour, but during these hypothetical chats, all you need to consider is the best possible version of the fighter at that designated time in his career. The more you do that, the more you see how close a lot of these fights get.