Re:2
The power balance between a startup and a VC is unequal compared to universities, big companies etc. The type of visa ascribed to each class is consequently different as well
For instance student visas under F-1 can have OPT extensions based on their course of study (i.e if you graduate with a CS degree, you don't need a visa to work in a CS field in USA) and this extension allows additional 6-months providence if in STEM studies
Companies are allowed only H1-B visas, in which if terminated for whatsoever reason, are only allowed 3 months grace to get another visa (NOT find another job). That means that they have to re-do all the paperwork and find a second sponsor willing to pay upfront as well. (that's why it's a big company thing, the company has to show a need for this worker that a US citizen doesn't provide)
People who give out Oscars don't give visas, you're mistaken on that. The class of visas you're alluding to (O-1 visas) are for special achievement in a recognized field particularly in sports, entertainment or academia. The individual sponsors their own visa, and makes a case of it through letters of recommendation and appeal. It's not enough to be a "founder of X company", there's a minimum about of press, articles published, conferences attended and awards/prizes INCLUDING awards from the applicant's home country (so they must have international level achievement)
What class of visas would investors be allowed to have sway over? The govt. could make a case that a startup visa is a loophole around HI-B1 because it doesn't nessescarily demonstrate a skillset not already owned by an American. In effect, for your case to work, YC would have to prove that entrepreneurship is not an American quality.
The other option is O-1 visas, but that assumes that your founders have existing press/awardship already given in their home country.