Mastering every intricacy of a language and its ecosystem has value but that’s not what most employers or customers care about or pay for. My customers almost never care about the language or tools I use, or quality of the code, or anything programmers obsess over. They care about spending their money to get more value through reduced costs or increased efficiency.
You can optimize to impress your peers, or to always have a job (or customers if you freelance). Depends on your priorities.
Programming expertise is largely cumulative because the basic concepts apply in every language. Someone with 5+ years experience with real C++ projects shouldn’t struggle too much with Java or Python.
