both apply to different people.
depends on both psychologic and physiologic factors.
some people are better at sticking to one set and defined thing, and working on and honing it, until they become very, very good at that one thing.
however, some people like to fine tune things to find the easiest way for them to improve, and practicing various things to become overall better.
this is sort of the mindset behind not having everyone be a flex player and having specialization. some people are good with having a large, set goal, some are better with many, smaller goals.