This is the part that bothers me. Why isn't it an option?
Standing up a new orbital rocket company was not really an option in 2000.
If Boeing can deliver 400 aircraft a year, why can't a startup deliver 6 in the next six years. I don't mean 6/year. I mean take 6 years to build your first 6. Or maybe it takes 12 years to deliver the first 6.
Then aim to deliver one per month for the next two years. Get FedEx and UPS and Amazon to fund you for the next 15 years. By then you could have two dozen aircraft flying real miles, building up experience and trust. Then you ramp to up to 25 aircraft per year for the next two years.
Sure, this means that after 20 years you still haven't replaced Boeing.
But Tesla didn't have to replace GM to revolutionize the industry.
When you become a real threat to take away 50 orders per year you cause visible activity among your competition. Just ask Bombardier.
(I wish I hadn't used Elon as an example twice in the same post, but it is what it is. Like him or hate him, his history is relevant when you talk about what is possible in giant established industries.)