You're certainly right that with a macbook you get a whole computer, so you're getting more for your money. And it's a luxury high-end computer too!
But personally, I've never seen anyone step directly from not-even-having-a-PC to buying a 4090 for $1800. Folks that aren't technically inclined by and large stick with hosted models like ChatGPT.
More common in my experience is for technical folks with, say, an 8GB GPU to experiment with local ML, decide they're interested in it, then step up to a 4090 or something.
"Should I upgrade what I have or buy something new" is a completely normal everyday decision. Of course it doesn't apply to everyone since it presumes you have something compatible to upgrade, but it is a real decision lots of people are making
