This is good advice to give college students, where it can seem like picking a major is signing up for a single-track life you can never escape from. But valuing narrowness so much is peculiar to academia. I left a PhD program for that reason — it takes a certain mindset to be happy spending your whole intellectual life doing one thing. Luckily, the rest of the world doesn’t operate in the same way.
You do have to be specialized enough to outshine every other joe-shmoe. But that’s not such a hard thing.
It was in small companies in particular that I’ve found a wide range of skills is valued; like coding and data analysis and graphics and copyediting. No, they don’t care about my medieval history certificate, but that’s what hobbies are for. A friend doing a start-up found the same thing. Yeah, he needed great coding skills; but also a ton of other skills. A PhD in CS wasn’t needed.