The Gnosis derives from the Quya but the Gnosis has been filtered through thousands of years of human scholarship. I think that the Gnosis practiced in the time of the books is probably very different from the Quya.
Quyan magic is suited to the minds of the Nonmen and Nonmen are weird by human standards. The Gnosis was developed and honed by men. There are probably many Gnostic incantations that are based on earlier Quyan formulas and that accomplish the same thing but the logic of spell has been changed to make it more accessible. Pieces of Quyan knowledge may have been lost and abandoned over the years. Also, humans have expanded on the Quya. They've improved old formulas and developed new ones.
In the end I'd bet that the Gnosis is slightly more powerful than the Quya. The Quya has become stagnant as the Nonmen have declined, whereas humans continue to tinker with the Gnosis.
Now maybe some of the old Quya that are still wondering around, who have all but perfected the gnosis after thousands of years of practice, might stand a chance.
The Nonmen magi who are still around aren't more powerful than human sorcerers due to the superiority of their incantations. They are more powerful than human sorcerers because they are themselves physically and mentally superior. They have inhuman stamina, inhuman intelligence, and many lifetimes worth of practice. They're almost always win, but the Quya is the inferior weapon.