The problem I have with that is that the Quincy are so pathetically weak. They need to steal Bankai to even be able to keep up with the captains. I don't enjoy watching fights like that. The arrogance of the Quincies pisses me off too. They're weak as shit, yet they talk bigger trash than Aizen did.
Quincys weak? I completely completely disagree. They don't
have to steal Bankais. They're just doing it because they can. The Vandenreich, being Quincys, despise the Shinigami. They would do anything they could to ridicule, humiliate, and destroy their pride, will, spirits, what have you. This war is personal to the Quincy. Even if they didn't need to steal their Bankais, they would still do it out of pure spite.
Just because the Sternritters have been stealing Bankais doesn't mean they aren't capable of fighting without them. Take the guy Kyoraku was fighting, for example. He didn't steal any Bankai but he was still fast and strong enough to take out one of Kyoraku's eyes. Haschwald too. He destroyed Ichigo's new Bankai with one strike.
When the Quincys first came to Soul Society, Byakuya himself said that they weren't enemies they could fight without busting out their Bankais:
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Just like Renji said. If the Quincy can steal Bankais, then they should have just not used them, right? But Byakuya risked using it anyways because they needed to.
Byakuya is an arrogant guy. He likes to talk down to his opponents and gloat. But if he of all people admitted this, then it means that they're pretty formidable opponents
On the flipside of my argument, what does it matter if they can steal Bankais? That's still a tool they have. We may not like it, but it's a part of their arsenal which makes it fair game.
To be honest, we've known since the very beginning that Quincys can absorb reishi from their surroundings and turn it into their own reiatsu - Ishida vs Mayuri. Stealing Bankais is, in a way, an extension of that ability. They're incorporating something external into their own power and using that to their advantage. I don't get what the big deal is. Nobody called Ishida weak when he was cannibalizing the buildings around him. Why? Because it was a part of his ability. It's the same thing with the Bankai stealing.