Let's take a look at what we have, when Hichigo interfered in Ichigo's fight with Byakuya, he dominated him until Ichigo stopped him. Vizard Ichigo has fully mastered Hichigo, and Ulquiiorra dominated him in his first release, while Byakuya may have gotten stronger than Ichigo, he hasn't shown the power to utterly dominate Ichigo like Ulquiiorra did, let alone in Segunda
To be fair, we can't judge that fight, considering a)He was fighting with Kenpachi, b) We didn't see half of the fight when Yammy got serious and c) Yammy is an entirely different kind of opponent than Ulquiorra, granted, he may be more powerful, but is also a much easier opponent for Byakuya considering their different ways of fighting.
Ulquiorra is much faster than Vizard Ichigo, should Byakuya fight him, I can easily see what happened to him in his fight with Ichigo happening a lot more
did everyone forget that not even aizen had seen his 2nd release ,that 2nd release actually made him by far the strongest espada plus he had instant regeneration and is very smart and can keep cool,i believe he just didnt want to be the strongest not sure excactly why but ulquiora can easily beat byakuya yammy was nothing in fact i think they let him be espada 0 just for him to stay behind thinking he was important truth is all he realy had is size and strenght but i am almost sure that regular hollow ichigo before his arrancar mask could have beat him no problem the real strong espada where 4,2,1 those where the strongest hands down i just cant believ any of u really believe that yammy is actually powerful lol hes pathetic,only reason he could touch ichigo was becuase ichigo only had partial spirit pressure and was incapable of hollofication due to the arrancar mask leaving him with a less than half strenght bankai i mean ichigos bankai can probably match any of the captians without bankai and surpasses or match a few using bankai