About RuffyxZorro. I think Oda shows that Ruffy is stronger through the fact that he always fight the big ones. That's not only because Ruffy is the main character.
I think Zorro couldn't have taken out the bosses with the strenght he had when they faced each one of them.
Not Croc, not Enel, not Lucci, and maybe not even Arlong (even if he would've been at full strenght that time).
Ruffy is just stronger. It's not by much, but he still has the lead.
"For Feanor was made the mightiest in all parts of body and mind, in valour, in endurance, in beauty, in understanding, in skill, in strength and subtlety alike, of all the Children of Illuvatar, and a bright flame was in him"