I think this statement was long ago amended to:

"you should learn a systems language, if you want to be a 'complete'/'well-rounded' SWE"

C was never the point (it was just the common low level language), the point was that just learning PHP/Python/JavaScript/Ruby wasn't enough to get a full grasp of everything that's going on, since they hide a lot of the warts from you.

I, personally, still believe this. That being said, you can definitely make a career out of doing nothing but JavaScript/TypeScript/React, PHP/Laravel, RoR, etc.