Wouldn't having deep specialisation in a particular field help you to gain a competitive advantage when deciding to go it alone and starting a company in that area?
Absolutely, but the more specialised, the more likely your skill is one part of a much bigger structure and therefore you're less likely to be able to leverage it as a solo entrepreneur.
For example, you spend 15 years becoming a lead engineer for a vehicle manufacturer. But there's very few ways you can then that into a solo business, other than consulting (which is no longer the same work).
Many countries - like UK - have restricted consulting type of business, where it's not possible to make profit, as consulting engagement has to be taxed as deemed employment, even if it is a legitimate business, when service is provided by the owner of the company. Pulling the ladders etc.
