Interesting point. I think job markets don't move as fast as technology itself. Just because a new framework comes out (and yes, in the web world, it feels like a new one pops up daily), doesn't mean an employer will say, "Ok team, let's rewrite everything in React, or Angular, or (insert your favorite new trend of the year)." A search for web development jobs will show openings for frameworks that came out 15 years ago. It's more important that a student learns to code and understands the fundamentals of problem solving and program design than worry about the latest frameworks or tooling.
HTML,CSS, and Javascript are never out of fashion. The only thing he teaches that is applicable to what you said is Ruby on Rails and even then Rails has a strong foothold on the market.
Systems that already exist need to be maintained. Why do people still write COBOL? Because it's cheaper to maintain an already in place system than to rip it out and replace it with the newest fad.
My professional experience says otherwise. There's always more work maintaining/enhancing sites than creating new ones.
By the way, Rails is the craze from maybe 10-6 years ago. consider e.g. [0] But it is still far, far from dead. Time flies, but not as fast as you suggest.