I can’t verify this myself because the Chromium codebase is far too much of an undertaking for myself to review.

No, but there are several people and organizations that can and do that would be screaming from the rooftops if there was some sort of telemetry that they could not remove.

I trust Mozilla/Firefox to be more caring about protecting my personal data than I do Google, who literally revolves around data collection.

You don’t need to trust Google because Chromium-based projects are not made by Google. They are forks of the open-sourced Chromium, made by completely independent organizations, explicitly for the purpose of removing telemetry.

People are seemingly incapable of understanding that Chromium-based browsers are not Chrome, nor are they Chromium.