Indeed. Here's why we know this isn't true: everyone has areas they focus on, and they aren't defined as "everything fast-paced that exists." You can spend literal years working on problems in the security space, or on web front end crap, or in audio processing, or object storage, learning absolutely jack squat about cloud, ML or k8s, and you don't shrivel up and die. I basically completely switch disciplines every time I job hop, and nobody's ever questioned me about keeping up with whatever fast-paced stuff I was doing two jobs ago.