Buying subscription and using it to build a distro would be against Red Hat Subscription agreement. I guess you missed all the drama of the summer, when Red Hat made it so.
You are supposed to say that we all have a right to an “exact” unpaid replica of the full RHEL distribution that we will explicitly not modify or improve in any way but instead directly commercialize and monetize. We have the right to do this because the above behaviour embodies “the spirit of Open Source”. If Red Hat tries to stop us, it is because THEY are evil and greedy.