This is actually my favorite kind of HN discussion. I think the added context is really interesting, despite maybe being a bit of a tangent. English is full of "orphaned" words and phrases that no longer make sense in general usage (no one ever refers to a "gamut" unless something is "running" it). I had no idea that "used to" was an example of this.

I think maybe the tone of your comment has a bit of "well actually" that bothers some people. It's the difference between sharing a fun fact versus policing correctness. The interesting point is that "used to" is weird, but not for the reason that the parent comment assumed. That's a genuinely fun fact that I enjoyed learning.