Instead of saying because of Byakuya, the espada must be leaps and bounds ahead of the other SS captains consider this. Byakuya is a NEW captain. I seriously doubt hes stronger than half the other captains - imho Soi Fong would own him since once you take away his speed hes really just got ... his bankai, and that can be evaded but i dont even think he could go that far before getting hit twice especially with Soi Fongs speed. So trying to make this theory is kinda like saying A > B, C > A, so C > A is way too simplified. There are other things to take into account.
Do I think any of the current espada could take on Shunsui, Zyuushiro, Shigekuni, Kurotsuchi, Kenpachi, etc and win... No.