Life seems to have two choice of strategies. You either specialise in a niche area or you broaden your outlook and cover all the bases. There are risks with both strategies but it seems to me the generalist one offers the most opportunities.
The construction industry is full of specialists: architects, surveyors, structural engineers, interior designers, builders etc. But it is technically possible to construct your own house. You may need people to check on your work from time to time, and if you make too many mistakes it can prove costly either in money terms or more seriously with implications for the health of the inhabitants. However it can be done.
Specialists come into their own when you want to try something different. A good architect will be able to respond to a challenging design brief by using their creative abilities to blend vision with reality. They in turn will work closely with a structural engineer to provide technical solutions to the new problems that arise from pushing the limits of construction. Materials specialists may also become involved. No generalist could manage this on their own.
Saying that, many project managers are generalists who are able to bring together specialists into combined teams for defined periods of time. They exist in all spheres of life and started to appear in their own right during the 20th Century. John Wolfe Barry might have been a possible candidate for this role if he had been born a century later.