Now that ad blockers have to be built out of declarative syntax that Google controls, the browser maintainers basically _are_ responsible for implementing the ad blockers. And would you look at that they're pushing back on community contributions and dragging their feet because yes, there is a conflict of interest.
They left alone other imperative-but-dangerous aspects of extensions, such as the ability for any extension to watch what you type into password or credit card fields on any website. Actually that sort of extension is even easier to write in MV3 and Google will still need JS-reviewing wizards to give a guarantee an extension isn't snooping your passwords.
I don't think there's a consistent position from Google if the claim is they want to improve security via declarative syntax. I think Google is full of shit.