I am one of those people; I have ~150% zoom on most sites, often higher. It's 240% on HN right now, which is my "default" for HN. This is not because I'm visually impaired by the way – I don't even use (or need) glasses – I just like it. I've been doing this since I was in my mid-20s and I just find it more comfterable.
I find these kind of reflows frequently make the page worse, not better. Even with a high zoom level the full desktop site usually works better than the "mobile optimized" site.
It's not uncommon that zooming will make the text smaller. You're at 140% and want to go a tad higher, so you go to 150% and bam: you're over the limit, the text becomes smaller, and now you need to zoom to ludicrous amounts to actually get the desired 150%.
The overall layout also often becomes worse. A common issue is that it makes the box in which the text is displayed too narrow, wasting a lot of space.
This is basically what's going on in this story: it's not that the website shouldn't work well on all different zoom levels or that it shouldn't have any kind of reflow at all, it's that it shouldn't give me a "mobile" site when the desktop version is actually still just fine. I think you've misunderstood this post a little bit.
In my own websites/webapps I generally take a gradual approach. If the screen becomes too narrow to display a certain UI element then tweak that element a bit, and do this individually for every UI element. This is quite a different approach than the "IF smaller_than(1200px) THEN serve_mobile_site". IMHO that's just lazy and bad design.
I usually avoid device detection, but do use it for a few things (e.g. <input type="date"> is ugly on the desktop, so it always serves a JS version for that).
A related note: forcing mobile UX patterns on desktop in general is usually not a good idea. Today I wanted to copy some text from the Dutch parliament website, and I couldn't as the UI element was one of those "swipe left/right" things, so actually trying to select text would swipe the thing to the left/right. I had to resort to the inspector mode to actually be able to select/copy the text.