Perhaps it depends much on the mind of the person; I don't think I could just focus on one thing forever. But while the new shiny tech guys may seem to have more opportunities, I believe the domain experts may get paid more and have more of their career time spent as "recognized leaders".
It's probably good that people are all different, and both types (and all in between) exist.
To analogize, if you are a general carpenter, you can always find work, but it will be at a lower rate. However, it will be varied.
If you are a fine cabinet carpenter, your work will likely be more focused, possibly more repetitive, more lucrative, and harder to find (you'll have to seek out the folks who need really really nice cabinets).