If a person is locked up in one feature/one product and unwilling to learn new things for the years then I do not think that person should be promoted. You can certainly give merit increases to keep up with inflation but that's about that. Ultimately, we all responding to market value of a person. That value remains unchanged for someone not learning anything new for years after the earned experience saturates. In many professions like doctors or pilots, experience never saturates and continues to increase person's market value however in other like cashier or barista that's not the case. So this opinion is job-dependent.