Providing the rockstars with a sandbox where they can do anything and work independently, while being shielded from all the processes and paperwork that slow them down (while also having people to pull that slack), is a fairly good method, but depending on the work that isn't viable. Their work has to come out of the sandbox at some point, and there will be some back-and-fourth which will probably put blocks on the team in that case.
I doubt there's much to do about the specific process that can be done to minimise the problems of the rockstars without also causing problems further down the ladder, without just starting to make exceptions like you said. It's probably just an emergent behaviour of processes like this intended to raise average quality. You pull up the bottom floor, but the roof gets lower as a result. You can find similar problems in schooling.
I doubt there's much to do about the specific process that can be done to minimise the problems of the rockstars without also causing problems further down the ladder, without just starting to make exceptions like you said. It's probably just an emergent behaviour of processes like this intended to raise average quality. You pull up the bottom floor, but the roof gets lower as a result. You can find similar problems in schooling.