I think it’s unlikely to become expert in all of those things. If you do, it’s over the course of an entire career, not to get started. I guess it comes down to how much expertise is “enough” for you. Naturally, if you split your time across 3 domains you won’t be as expert as someone who dedicated all their time to going deep in one.

In the context of a big company, I think it makes sense to have a specialized workforce. Why look for the one in a billion person that can publish top quality theoretic papers and then implement them on distributed gpus in an optimal way while also building simple Random Forest models for your business? I’d rather that person do more of the most valuable thing, and then hire someone else to do the rest.