This.
Jack of all trades shops wont make it big. Unless you have the very best group of employees. then your top notch full in house shop, kind of like Austin Speed shop and JJ. (less paint, they dont paint so its not a perfect example) As in one guy ONLY paints, one only does body work, one only does metal work, one chassis and suspension, one motor, one trans, one machinist, one welder… thats the only way a “do it all” shop will ever be big time successfull. Its simple why. If you are not the best at the potental jobs aspect in the area, what makes them want to go to you over someone down the road that is just as good, but only does that one aspect? Cost usually, and that will drive your prices and value down to get the customer, not up.
Example Paint. Shop A has an alright painter and could probably do the job, but Shop B only paints and has a better painter. You are choosing shop B. BUT if shop A has a damn good painter, none of the other aspects they are also good at matter you still would go to shop A, especially if you think down the road you will want more than paint.
Point; if you want to do it all, you better be damn good at it ALL. Or specialize and stick to it.