For me the courses didn’t boost creativity in me as much as I wanted them to but I think they did help those who weren’t previously creative. Re: your 2nd question: I think the network prepares you more effectively than the courses for building a start-up.
Something I need to clarify here — at IESE we were taught with the case study method majority of the time. In those classes the students speak more than the professors. We’re sharing insights, experiences, strategies with one another. So when I say “it’s the network” it can mean the network you build and take with you beyond graduation but also the network from which you’re learning before, during and after class each day. Hope that clarifies.
The courses (the course lessons I mean) help more with once that start-up takes flight and it’s time to hire and manage.