I find it interesting that your reason for Conor having a chance is the exact same reason I have for him having no chance at all: This is real life.
hahaha
No, but it is not only that.
Conor is in his prime, and he is a fast, powerful striker.
I know, it is not a boxing guy, and compared it might be rustic, but what matters, is that he got speed and power.
Now Floyd is obviously out of his prime and don't forget, speed/reflexes is the first thing to go.
Floyd is retired! And that means he did not train for the past few years while Conor was very active fighting in MMA.
Floyd will also be over-confident, and that means he might not train as hard as he used to, push himself as much as he did before, etc. Plus he might do things he didn't normally do (i.e. go for the kill) which opens more chances for Conor to capitalize.
So for all that, I do give Conor more of a chance. Again, not saying it adds to a lot. Maybe 0.02% higher chance.
But that means he has SOME (however unlikely) chance to win.