Brave is not spyware. That website you linked is horrible and full of misinformation. They also claim that Firefox, and even Tor Browser, are spyware. They act as if any and all connections a browser makes are automatically bad and used for spying/tracking.
I won’t disagree with the other criticisms of Brave that you made, but just wanted to point that out. That website is just highly unreliable and makes verifiably false claims about the browsers it reviews.
Yeah, Shizuku opens up a massive attack surface through ADB. ADB can do a lot to your device without you even realizing it in a lot of cases, and you’re basically giving ADB access to Shizuku itself and any apps that use it (which could be exploited) at all times, so its very risky. Its pretty dangerous and definitely best to avoid an app like this.