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 :)