I don’t know what he means. Or thinks he means. There is no Protein:Fat ratio. There are absolute protein requirements, and there are absolute minimum fat requirements, but there is no related ratio, because while protein requirements are relatively static for a given category horse, fat requirements can vary a lot. Horses evolved eating only about 3% fat, but some horses do need more than that in their diet for a variety of reasons.
Growing horses need a LOT of protein relative to their body weight. A yearling needs about the same protein as his adult self in moderate work. That means the total protein as a % of his caloric intake is a lot higher. So, the more protein-rich feed he can get, the better.
I have known and used him exclusively on my horses for 20+ years so I trust his judgment–even if I can’t remember exactly what he said now
Once my boy is done growing I think my RB alone will be more than sufficient for him.
RB alone, or RB + some alf pellets, is a calorie issue, not a nutrition issue. If you feed the RB according to the age, nutrition is good (assuming decent enough forage). If he needs more calories, add alf pellets (or almost anything, really).
My homebred was put on a balancer as soon as he aged out of the milk-based phase, and he’s never gotten a regular feed. He’s either gotten just a balancer, or just a v/m supplement (HorseTech High Point Grass) when he gets too heavy with Spring/Summer grass, or a balancer + some small bit of alf pellets for additional calories when in those early in-between stages. Nutritionally, there is no aging out of balancers. But a horse can “calorie-needs-out” on either end