A jazzband is like a team in a startup
Everybody has to be an expert on his instrument / on his topic.
Only the team can execute a performance. So, it makes no sense to play alone or to have everybody playing the same instrument.
A good performance includes the product, the setup, the audience, the customer. You have to agree on the product. You have to enjoy to perform. Not only to play rehearsals in a cellar or to produce a product without going to market.
The audience / the market is the only one to be allowed to give you feedback. No trainers, no consultants.
Within a gig you feel if it is good our not, because you get immediate feedback from your audience. They are contributing to your product. That is why startups have to get into direct communication with their customers.