People really need to kill that notion that telemetry is automatically bad.

I agree with you. There are projects where I opt in and enable telemetry, such as KDE or opt in the Steam survey whenever asked. Steam in particularly does a good job on representing the data in front of me that is sent back.

If the information they are collecting is minimal, as non-identifiable as possible and actually being used to help develop the browser, it’s a good thing.

Problem is, its a bit ghosty what is actually being collected and sent for most people. Is it really non-identifiable as we think now? You know, sometimes later things get revealed and suddenly the entire time you was living in a lie (Privacy mode thing, where people had a misconception). If its enabled by default, this is especially bad, because this should be opt in. Telemetry is not bad per se, but it is bad if its enabled without user agreement.

opt-in telemetry is pretty much useless for trying to understand the majority of your user base.

Wrong. In example Steam does an opt in and the data is somewhat representative. You don't need to watch every user to know what is going on. A small sample is enough to understand the majority of the user base by extrapolating the data. Telemetry does not need to be exactly perfect to be useful, it just needs to help understanding trends or huge bottlenecks.