I agree with this article, but with one caveat. Don't be the guy that becomes the designated INSERT_OLD_TECH_HERE guy in the office while the rest of the team is working with the cool modern tech that has a lot of jobs in the market, don't pigeon your career by becoming an expert in legacy tech, like COBOL, RPGLE or FORTRAN. You'll find yourself in a position where you'll get fired and won't be able to find another job because there aren't many jobs for your skills and because companies only want to hire people with years of experience in the tech they're using, be it javascript, java, go etc.

And also these legacy techs don't pay that much in general, for every consultant making bank fixing COBOL bugs there are probably dozens or more COBOL developer making less than a javascript developer, so you'll find yourself making less money than a kid with a 3 years of experience in web development, and when you go out in the market trying to switch jobs, you'll have a hard time finding a new job or salaries will suck. Don't be stupid and become the fall guy to keep the legacy debt going while everybody else in the company is learning the in-demand cool stuff and padding their resumes with hire able skills. You will regret it.