I don't think it comes down to demands. Demands can be accepted or refused before a fight commences.
It just comes down to pure boxing ability. Marquez has(or very likely had) the answer.

So if Pac lost at Lightweight, I'd say it was simply because the better man won... Yet again.

I doubt Pac would loose though. I think Pac would annihilate him now. (if he could make 135)