Its honestly beyond me why you would ever(AND I DO MEAN EVER) think that kenpachi would even stand a chance against Aizen. Shikai or no shikai.
Well its a good thing that fights in bleach aren't just about people blasting each other with kido so Aizen>Urahara but i will address your misunderstanding of kido.
Urahara isn't necessarily better than Tessai or Aizen. He is just a hands on expert of the hougyoku(which means he can come up with counters for it) and he is a genius. Literally the smartest person in the show. Tessai could have taught Urahara everything he knew but Urahara would have still looked like a bitch to Aizen if that was the case.
http://www.mangahere.com/manga/bleac...c316.2/12.html
The reason Urahara even had a chance to hit Aizen with his super kido cuffs was because Aizen didn't give a damn about what was going on. He thought he was invincible and nothing could hurt him, he was literally just letting things hit him. If it wasn't for the combined efforts of Urahara's creative kido genius and Ichigos mega plot haxxx to hurt Aizen then he would have gotten away with it.
Also how are you even judging expertise in Kido? Like what makes somebody the best? Based on the numbers Aizen used a higher lvl kido than Urahara and Yammato used the seemingly most destructive one. The only reason Urahara had such a hax kido was because he was a genius, he knew about the Hougyoku, and because Aizen got cocky. So i would say they are around the same level but i will give Urahara the edge.
Aizen has twice the spiritual pressure of average/mid captain; Manga fact. Aizen is faster, more versatile, more intelligent, more experienced(been around longer), and has comparable durability and spiritual pressure to Kenpachi; Manga fact. Kenpachi is in no way, shape, or form a threat to Aizen. You wanna know why people throw around his name like he is a god? Its because there are literally only 2 Canon people stronger than him at the moment. Yamma and Ichigo and the former is Pre-Hougyoku while the later doesn't apply anymore.
Kenpachi struggled against the 5th esapada. Even if he had gone all out against him from the beginning he would have only won because he was fighting a weaker version of himself. The 5th esapada was a "hollow version" of Kenpachi. A straight up slash and cut tank. Nothing else. Kenpachi will always win against opponents like that. Aizen isn't that kind of opponent.
Aizen brought down Grimmy to his knees with a mere flex of his spiritual pressure. Yamma was willing to kill himself and the entire gotei 13(that was there) in order to kill Aizen. He made Vizard Ichigo his bitch(whom undoubtedly has comparable if not higher spiritual pressure than kenpachi). He tanked a full on direct Getsuga tenshou to the chest and then went on to fight Isshin(another person stronger than kenpachi).
Aizen might not have been able to beat all the captains and vizards like he did without his Shikai but he could have beaten anyone of them one-on-one save for yamma without it(as long as "big 3" didn't use their bankai).