1. While it's likely that Yamamoto defeated Yhwach, 1000 years ago, there is no proof that he did that.
2. I respectfully disagree with Aizen or Ichigo being stronger than Yamamoto.
That didn't refer to him being sealed but to Hogyoku rejecting him.
Ichigo said that AIzen deep in himself wanted to be just ordinary shinigami and not some guy with hell broken powers. That's why Hogyoku rejected him. That's my argument.
It is your right to think, that Yamato was stronger. But you are doubting that he beat Yawach ?
That's why it's an asspull. A stupid plot device to beat Aizen. Aizen was unstoppable, he could evolve from anything. Kubo didn't know how to beat him. Just like Kishi didn't know how to beat Madara
Are we supposed to say Madara loses to the likes of Sakura because Zetsu beat him? How does Juha Bach beat Aizen without killing/sealing him?
That's why it's an asspull. A stupid plot device to beat Aizen. Aizen was unstoppable, he could evolve from anything. Kubo didn't know how to beat him. Just like Kishi didn't know how to beat Madara
Are we supposed to say Madara loses to the likes of Sakura because Zetsu beat him? How does Juha Bach beat Aizen without killing/sealing him?
I said likely Yama defeated Yhwach, but it's not 100% confirmed, and there is possibility that he didn't and that Yhwach lost because he hasn't had souls to absorb or some other way.
Aizen wasn't unstoppable jeezus. If he was then why was he afraid of Ryujin Jakka? He created WW specifically for the purpose of sealing Yamamoto's flames. That shows how scared he was of the Zanpakutou. He even admitted that if he was t 1v1 Yamamoto, he'd lose as Yama's Ryujin Jakka is the most powerful Zanpakutou when it comes to pure destructive force.
That's just his shikai right? Now just imagine Zanka No Tachi vs Aizen. Aizen thought that he had subjugated the Hogyoku but it was actually the other way around. The Hogyoku possessed it's own will and it had a mind of it's own derp.
Enough ranting, Juha > Any form of Aizen. And this is base Juha that we're talking about mind you.