Why do you need a level playing field? Only if you are playing something competitive that requires even starting conditions (which is where the expression comes from). Is the North American (or European, or African, etc.) teacher competing for students? Seminar invitations? Youtube hits?
I just don't see why it is so important that the process inside Japan and the process outside Japan have to be exactly the same (and "fair").
If we apply the same principles, then it shouldn't take so long to get a black belt outside of Japan. It took me 6 years to get to shodan in North America. In Japan, I've heard that it can be done in two! It doesn't matter to me, it's just different, that's all. In fact, internationally, a North American rank might be more highly respected than a Japanese person's because people know that the standards are applied differently. Same title, different application, different meaning. Thank Yamada Sensei I suppose!
I think we agree that the intrinsic benefits of training, testing, teaching, or running a dojo are more valuable than the external recognition that may or may not be bestowed. Still, I see your point that if you have an ambition to receive the title and deserve it, but are unfairly denied, it would be frustrating and perhaps discriminatory. I just don't see evidence that this is what is going on.
As I said, I have a bunch of examples - but I'm not going to list names here.
In any case, if you're content with an organization that treats Japanese and non-Japanese differently then that's fine - but many people are not.
I'd note that the long time to shodan in North America isn't mandated by Aikikai hombu - that's a decision by the local North American instructors.