I don't share these kind of experiences. I try to maximize white skills, but I do use grey skills to boost my training. So most of my players white skills are around 150-160 and grey skills around 50-70 maybe. Only best players reach 'mutant levels' when they are around 30yo (grey skills 1, white skills 200-400). I have played for years like this and I haven't noticed any change in success. My best players score in any kind of game just the same.