The solution for the (as of yet) small group of people who cares about these things is very simple: community driven forks.

With the bonus that you also get a set of great (and per fork different yet handy) features.

These include:

Waterfox (Firefox) - https://www.waterfox.com/

Zen Browser (Firefox) - https://zen-browser.app/

Librewolf (Firefox) - https://librewolf.net/

Helium (Chrome/Chromium) - https://helium.computer/

Ungoogled Chromium (Chrome/Chromium) - https://github.com/ungoogled-software/ungoogled-chromium

Also as one of the major players, Vivaldi already made a stand against AI and forcefully including (agentic) AI in the web browser: https://vivaldi.com/blog/keep-exploring/. It's a Chromium based browser with a lot of nice features and deep customization options: https://vivaldi.com/