My point was that I had reconsidered my original position.
Altair does have the advantage in stealth, but that also depends on where Cu is. A lot of the times, being a figure of Irish Mythology during Medieval times, means he was typically in wide-open areas, as a constant traveler, which effectively removes the "stealth" option (If I remember this correctly. I haven't read these stories in many, many years).
But either way, My point is that as long as Cu can survive the first "jump" from Altair's stealth attack and engage him in combat, he will win. The key to that is -
A: Location
B: Cu's awareness of Altair being after him