It's definitely good advice to be mindful of one's needs. I have my own personal anecdotes about getting burnt by underestimating my
actual needs when attempting projects like daily driving an older laptop.
At the same time, keep in mind that the biggest tradeoff tends to be convenience. For example, a YouTube script plus local video player, such as MPV, works a treat on these older machines. Even if some video formats don't work great, you a) actually have an option for converting [0], and b) you are dropping all of the cycles spent on the non-video-watching parts of a YouTube video page.
Yes, that tends to make watching a 10 minute video kind of annoying when you spend a minute or two just on the overhead of downloading/opening/deleting it. Personally, I've sometimes found that to be a subtle push to read more text-based content instead of watching a bunch of videos. Similarly, it pushes me to favor longer-form videos that might involve more information and/or subtleties that the shorter videos might skip over (perhaps largely for SEO reasons).
All of that might or might not be a net-positive or even a possibility depending on needs, of course.
I've found a lot of personal motivation and fulfillment by looking for those sorts of alternate ways of doing things. Sometimes, slowing down (in more ways than just FLOPS) can lead you down rabbit holes that are not only fulfilling and interesting, but educational. [1]
Your point that it's bad advice to "just buy an [old] used laptop" definitely stands, but I'll just amend it with the caveat of "... depending on your needs/uses". To each their own.
[0]: There are also in-browser tricks/plugins for making the YouTube site itself lighter, but personally, I find throwing more instructions into the browser to be somewhat counterproductive. A bit like calculating how much extra fuel you need in order to carry the additional fuel, etc. The tradeoff is convenience, of course.
[1]: I'm also lucky to no longer have to deal with things like customers breathing down my neck with deadlines. So if I spend an extra 5 minutes doing something that used to take me 2 minutes, that's fine.