You people are so ignorant. Kishi created Gai and Kakashi as "Eternal Rivals". Do you seriously believe that a storyteller of Kishi's caliber would create the concept of "Eternal Rivals" if it didn't mean anything?
Kakashi and Gai have yet to fight each other, and for obvious reasons we'll never see it. But what Kishi's been trying to imply ever since he introduced the two is that they're neck to neck with each other.
It's not about which one of them has the Sharingan, or which one of them can open the most gates. The stronger one of them gets, so to does the other one. This is what Eternal Rivals mean.