> but they will probably earn less as they won't ever be domain experts

I disagree.

I've rarely seen any programmers that are domain experts, most of those domain experts are actually hired in a consultancy role.

As they work through the projects programmers can become very familiar to a specific domain but in general that's not their job and they will be treated as such. They will be consulted on implementation but less likely, if at all, on strategy. Which is what I would expect from a domain expert i.e. a consultant.

The highest paid programmers move jobs most often the lowest paid don't that'll tell you what becoming a domain expert means for a programmer.