that's just a waste of money as piston experience won't do much abroad
And that's a bit of an ignorant statement really.
There is no substitute for experience and if you want to work as a professional pilot..well you need to work as a pilot flying whatever you need to fly in order to gain experience.
Do not underestimate the value of instructional hours.
And you cannot work for a Regional with an F1 visa.
There are only 2-3 visas that lead to the issuance of a green card and the F1 is not one of them.