Firstly, they all came to the use of those techniques after having been through years of work the 'hard way', often being able to play to a conservatoire standard, and had a very extensive grounding in the tradition that came with that. Then they owned* or designed the thing they were asking to 'do it for me' and could modify it at their discretion, effectively making it an integral element of the composition. The prior training was crucial in getting anything good out of any of it IMO (high level reflection based on canon knowledge and deeply considered personal sensibility, etc.)
* I suppose in the early days, running on an mainframe would belie the definition of ownership per se, as it required access and was limited to that specific machine/institution, but then we are talking about a time where personal computing wasn't available.
* I suppose in the early days, running on an mainframe would belie the definition of ownership per se, as it required access and was limited to that specific machine/institution, but then we are talking about a time where personal computing wasn't available.