Having a niche is a good way to get your first and probably second promotion. Be good at a thing, get promoted to senior person of thing, maybe manager of thing. At this point you don’t want to be a specialist anymore if your goal is promotion. You want to be a generalist and know how things generally should work and be a good communicator. It helps if you are likable. The switch is hard. It is hard to give up what you are good at and hard to get people to see you are good at other things.