Agree that you need a balanced set of skills. However the advice in the article is pushing it too far.
Being a generalist is great in terms of broadening you career options, at an early stage anyway. But until you truly master something most of the higher tier opportunities remain closed to you.
These opportunities are much rarer and often not advertised. But the competition is also less intense and arbitrary. It is also in human nature to enjoy getting better at something. This path is actually not as hard as people think, and way more fun than keep picking up new mediocre skills.
Being a generalist is great in terms of broadening you career options, at an early stage anyway. But until you truly master something most of the higher tier opportunities remain closed to you.
These opportunities are much rarer and often not advertised. But the competition is also less intense and arbitrary. It is also in human nature to enjoy getting better at something. This path is actually not as hard as people think, and way more fun than keep picking up new mediocre skills.