They should be. The problem is that there are very little barriers to entry to these start ups and as such, pretty much anyone can start one and have a visa.

The problem with setting benchmarks are where do you set them? There is already a program know as the EB-5 program that requires you to invest $1MM ($500k in economic development zones) and create 10 jobs and after 3-4 years you can get a green card.