No, it’s how specialization works. True, as you do one thing more, you get better at it. This inherently disincentivizes jumping around and learning multiple skills, if we tie that to earning ability within capitalism. This does not have to be how we assign value, or earning, however. We could do any number of things differently, to incentivize different things.
One radical idea just off the top of my head would be pegging earning to age. Specialists get to specialize if they love a particular thing, and it won’t hurt their earnings. Jack of all trades still finds earnings more aligned to their actual worth to society - flexibility. Right now, being an okay person at everything is pretty crappily rewarded, because you only earn more by doing something REALLY well.
Again, this is just off the top of my head. I don’t think it’s necessarily the way to reorganize earnings in our society. It’s just an example of how labor doesn’t necessarily intrinsically have to lead to specialization earning more.