What You say is true but we have to see that GTs are cars of high class, expensive, fast with very big reputation. These cars must be faster than some B-segment shopping bags from some Korean carmaker but they are not. It doesn't work to pretend that it's no problem because it is a real problem and main reason why manufacturers don't give a shit about taking part in rallies. I know some people from Porsche, they are very proud on their cars and they want to beat anyone in their way - be it in Le Mans, on Nordschleiffe or wherever and they don't care how much it costs. They can't accept entering a battle which is lost already before it started.
There's only one way to bring GTs fully in rallying - to allow them to win. That will naturally make them a lot more expensive but it would bring the manufacturers in. After that it is possible to introduce something like "GT light" or whatever as a kind of gr.N GT level. I can't see any other way how this can work...