We have raised Cornish in the past and that is exactly what we fed them. They don't get the chance to get older for anything else to be necessary. We also gave them fruits/veggies as treats, but they didn't much care for those. In my experience it does not affect the flavor of the meat as it's grain based. So it's fine. We process our Cornish at 12 weeks while monitoring feed, and end up with a 0% mortality rate, which I've heard is wonderful compared to most. Keeping them on starter is the perfect way to go about it. They are getting the nutrients they need to grow and stay healthy. Good luck!