> a) Most adventurous student entrepreneurs don't really MUST need a founder visa, they can use OPT. I think founders of Stripe did that.

Founder of Stripe here. Not disagreeing with anything you've said, but I feel I should point out that OPT is far from ideal: it doesn't last very long, it requires the job is related to the field of study, full-time work is permitted only during vacations prior to completion of a degree, etc. Still, it can be a useful stopgap in some cases, as you point out.