TV certainly didn't make radio irrelevant, radio is very relevant in situations where you can't look at a screen, or would prefer not to. It's also much lower bandwidth, takes up a lot less space, uses a lot less power on the receiver (even compared to say a modern mobile device) and audio only content is much cheaper to produce.
I've heard it argued that podcasts make radio obsolete. That is more plausible.
I've heard it argued that podcasts make radio obsolete. That is more plausible.