Breh did you watch it or just skim through it?
Aizen was legitimately stronger than those Captains and former Captains and that's before you take into account the Hogyoku. His shikai basically makes everyone you named expendable, including Kenpachi and Byakuya. They wouldn't get one shotted like Hitsuguya but they definitely would have gotten their wigs pushed back.
Aizen had been plotting on the throne for well over a century and then he executed flawlessly.
Even pre-Hogyoku, the only people who were fukking with Aizen was Yammamoto and Gin