especially when you consider that one of FF's target user bases are people who turn off all telemetry

A couple percent of Firefox's user base turn off telemetry. That is a target group, but they're hardly representative.

(I'm not bullshitting. I worked for Mozilla for 25 years, including in the Netscape era. Brendan Eich and I built the Mozilla 1.0 roadmap. I was a co-creator of Firefox along with Blake and Ben. I was Firefox's PM at Mozilla when we deployed telemetry and I was a Firefox and A11Y PM when me and Andre Natal introduced local LLM-based language translation to Firefox a couple years ago (Nightly only, release came last year after I left.) If those credentials aren't enough to make my claim believable, then I don't know what else to say.)

It's definitely believable, defaults are very powerful (I'd expect a higher number, but not a very big one)

Though out of curiosity - if someone turns all telemetry off, how would you know of this use to count?

Yeah, though telemetry wouldn't help since this level of attention to UI design doesn't (practically ) exist, and it's unrealistic to expect it from FF, so the next best thing is allow user configuration.

Also you can even have a dynamic sorting section part within some menu based on how often you use a given menu item or depending on which profile you're using etc.