Scott Adams (creator of Dilbert) has this concept of a talent stack. The idea is you want to develop talents that are synergystic. So for example, web development might be one talent, which can get you in the door. But if you add database development, backend technologies, etc., now you can be a full stack developer. But if you go further afield and start developing public speaking skills, or people skills, now you're moving into a lot more possibilities. Point being, if all you did was focus on being really good at web development you plateau at "valuable employee". So I would say that developing talents outside of your core competencies is absolutely critical.
I would say intense focus on one thing reaches a point of diminishing returns. The key is to recognize when you have mostly tapped that vein and develop something else. That doesn't have to be a github project, often you want something far afield, especially to avoid burnout. it can be speaking classes, or improv classes, or even fitness, or electronics, or whatever, anything that helps your stack.
I would say intense focus on one thing reaches a point of diminishing returns. The key is to recognize when you have mostly tapped that vein and develop something else. That doesn't have to be a github project, often you want something far afield, especially to avoid burnout. it can be speaking classes, or improv classes, or even fitness, or electronics, or whatever, anything that helps your stack.