Separation is fine, its pretty essential really. We dont have any issues with it. The problem we do have is small kds getting declared on and nailed by massively larger kds, this was quite a common problem.
I seriously doubt that the top kds will now be unable to successfully play to chart because kingdoms that are, at a minimum, 30% smaller than them can dictate their age with ease. This hasn't happened with a wider declare range and I don't see it happening now. The argument that with a 50% range you could declare on them is just quite a lot of bull****, the gains would not outweigh dicing and would result in a net loss of acres so kingdoms that wanted to win would never declare down to 30-50% smaller than them.
Anyway, lets go with the idea that there is a valid point here - the tighter declare range allows kingdoms that are 30% smaller than you to mess about with you a lot. Why are you now unable to deter them?