User blog comment:Sicarius001/Royal Guard and Eighth Division Captain/@comment-8589859-20130423081917/@comment-5551986-20130503231917

"The main power of the Vandenreich is in their ability to steal Bankai. Without this, the Gotei 13 would have taken them out without too much effort. Sasakibe probably still would have died. He doesn't seem to have fought much, if at all, in the past 200 years. If he had been practicing with Bankai, it was somewhere that he could do so without anyone noticing the weather changes. 8 days ago by RobertG22"

You forget that the Quincy could use Vollstandig, Uryu defeated Mayuri's bankai without using Blut vene or blut arterie as far as we know, even if Mayuri did underestimate him a little. Vollstandig is apparently stronger than Uryu's version. The Gotei would still have struggled a deal, it was stated by Byakuya they are not the type of enemy that can be defeated without a bankai. But it still isn't a guaranteed victory even with that.