Much-needed information in a world who has been taught calorie restriction as the only way.
On the other hand, the closer you are to your genetic potential as an athlete or competitive bodybuilder the harder it is to lose the extra fat, partially because there is not much fat to lose in the first place; partially because the muscle growth potential diminishes over time.
Any advice for these athletes?
The true answer is anabolic-steroid. otherwise you will lose perfomance, muscle mass. You must be genetic freak to escape from that but this is like 0,1 % chance to get this. I know this maybe sounds ridiculous but this reality.
Fat loss is not going to be affected by the genetic potential of muscle gain. Fat loss can be achieved with correct manipulation of diet and physical activity at any stage. When it comes to muscle gain once you have reached genetic potential, of course, there is not much you can do aside from taking anabolics. But very few people will ever reach their true genetic potential. Those few who do will most likely be at the top of the athletic chain and won't be bothered by such question anyway :)