I'm not sure why, but I somehow saw this being a good fight. This battle is to the death, and both characters will be fully equipped and fully upgraded. They will start out in direct conflict, but they can later utilize stealth.
And Ezio had Eagle Vision by the time of AC: Revelations, it allowed one to focus on a target and sense approximately where they had gone, or inversely, where they would go.
Ezio had Eagle vision all along, and he'll most likely need it if he really hopes to win. Sly has him beat in stealth and mobility, but Ezio is better fighter and killer. They both have more of something to offer than the other does. It's really just a matter of how they can apply it.
He had Eagle Vision from childhood up to Brotherhood. In Revelations he developed it into Eagle Sense. It allows him to pin point who he's after, follow trails and future paths, follow smells and heartbeats.
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"Gonna need more chloroform..."
"If you look down on us, judge us, condemn us... then you shall fear us!"
And to counter that, I'd point out that Sly is an acrobat who puts Ezio, a marvelous athlete and combatant by human standards to absolute shame. Sly's strength and agility exceed human limits by leaps and bounds, as Sly is easily capable of knocking enemies twice his size into the air with a single hit and slamming them up and over his head, as well as literally running circles around them. On top of that, his gadgets and special powers give him an edge that not even Ezio's lifetime of experience and Eagle Sense would cover.
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All hail Scythe, King of the Sigs.