I think that's a much better advice than any I found from a cursory read of the article; at least with my limited experience with friends. Most of my acquaitances doesn't seem sufficiently agressive with salaries -- they're mostly worried about having a job, a "good enough" pay, and that this job doesn't suck too much. That's ripe for exploitation -- if you don't actively demand and seek the best deal, you're going to be paid the minimum you can to just scrape by and definitely won't get wealthy. You don't have to own a business to be relatively wealthy (I'm taking 'wealthy' to be relative because the threshold for wealth is indeed much higher in developed countries).
Also I think being wealthy is completely beside the point; it doesn't make too much sense as an objective. The article tries to make the point for wealth being ethical; but in any case ethical are possible consequences not the accumulation of wealth. Health, general satisfaction (including from making ethical choices) are what really matter. That does necessitate some wealth, but in general any wealth threshold is not necessary nor sufficient for those prime goals.
Those two points may seem contradictory, but it's not because wealth is a non-necessary correlated variable that you should just leave it at the table. Get all you can from your employer without compromising on what matters (and hence obtaining the conveniences and securities of wealth while retaining life satisfaction).
I'm not going to venture into defining life satisfaction, but I do think it's good to ask yourself from time to time. For me it is having decent amounts of free time, being able to help people, having fun socially, producing beautiful/impactful work, etc. -- but it could include whatever you deeply enjoy.
The abundance of contradictory points indicates that things aren't really cut and dry in any sense and this advice boils down to the same thing all advice boils down to: YMMV.