As you are finally realising - the law, past practice and morality is not restrictive in putting sub 500 hour people on the flight deck - it is actually the insurers who both allow it and constrain the mix, the proportion of them at any one time. The market, not the national authority, is in control. Even as a PPL it is the insurance industry that actually controls what you can own and fly in the States - not the FAA.
It's rather alarming and more than sobering to realise that insurers, statisticians and actuaries
have more commonsense than Air Regulatory Authorities and Airline Flight Operations Departments.
Is it any wonder that accountants run airlines? We professional pilots seem to have given up any moral right to ensure safe flight operations, and we should be rightly and eternally damned for relinquishing this public safety role to mere bean counters.
We should hang our heads in shame.