Duniak
1. You say we don't know about Urahara's Bankai? Do you know about Aizen's Bankai? Or do you know about Yama's Bankai? Yama's Bankai alone seemed to be enough to destroy SS with all the Captains who were there and this Bankai now belongs who the guy who was actually able to take down base Yama who seemed to be stronger in base than base Aizen... So no way Urahara's Bankai would make that much of a differense.

2. So what? Yoruichi's fits aren't that impressive. She was a bit faster than Soifong and a bit faster than Byakuya, but the same Aizen made a fodder treatment of Soi Fong and many other Captains who seemed stronger than Yoruichi. Also Yoruichi isn't the best in hand-to-hand combat. The same Yama or Tessai seem to be way higher in that department.
3. Again... It's Shounen manga! Here intellect doesn't play that much of a role to be a desisive factor. Aizen was intelligent, but he was strong enough to be able to take down practically entire Gotei in Shikai-Bankai in just his base form... Also Urahara's intellect lies only in the field of inventions. Aizen seems to be better in terms of planning and tactics.
4. Well, Isshin seems to be able to do the same as well. The same way as Yama and Tessai is obviously better than Urahara in Kidou...
5. Well, Kubo stated himself that Shunsui could do the same thing Ichigo did against Hougioku Aizen with his Bankai, but it wasn't his role to do it, but Ichigo's. Does it make him fit to be the final villain?
Also Aizen didn't want to dodge any Urahara's attack. He wanted to test his new form. He wouldn't have done it, when he was a normal Shinigami. Urahara himself stated it.
So it doesn't make Urahara strong... Not even close to high tier Captains. The same Urahara in his Shikai couldn't do anything against Base Ulquiorra, while Aizen could have taken entire Espada down by himself. His Reiatsu was so strong that he made Grimjaw fall on his knees infont of him... Compare the differense.
dex
Well, I agree that Juha Bach might not be the Final Villain.

I just pointed my thoughts why Urahara can't be the one...