This approach fails when hard obstacles start presenting themselves. The founder is not bought into the idea so much that he/she cares to see it through. The VC

This approach fails when hard obstacles start presenting themselves. The founder is not bought into the idea so much that he/she cares to see it through. The VC sees it as 1 of a large portfolio of ideas. And if you look through the history of startup ideas, (as you've said) the execution helps bring the team unique insights to help with pivots. I've seen this type of thing work inside companies though, where people work in an incubator like YC, except there are shared resources and the incubator is an umbrella company.