I've been there and I know it's true. However, becoming an expert on something is still valuable as long as that something has value outside the company (ie: y

I've been there and I know it's true. However, becoming an expert on something is still valuable as long as that something has value outside the company (ie: you can advertise that kind of expertise in an interview). So becoming an expert in something is valuable and if you realize you've become the "load-bearing employee that never gets promoted or otherwise has company mobility" then it's strong signal that you need to start replying to recruiters.