I have a 9 month old 25 lb. male corgi. He is not the best eater, in fact he is very picky. He eats about 1/2 to 1 cup of Fromm's per day. Usually mixed with yogurt or broth. He's very active and he's in perfect health according to the vet. From other corgis I've seen and one that I had previously (adopted as an adult), he looks extremely small in comparison. Although he is probably considered normal in weight for his age, he has a thin and athletic looking shape. Not thick like the signature corgi look. When do they usually fill out?
Since he's on the all life stages food I think it's normal for him to seem like he's growing a bit slower, but that's really what you want. Nice steady slow growth is better for their health in the long run than really fast growth. I've been feeding the ALS Fromms to my cardi Luke since he was a pup, and I definitely noticed he grew quite a bit slower than my pem who got puppy food. Luke is just over a year now and he is finally starting to fill out. He sat at 26 lbs for like 3 months, and then all of a sudden jumped up to 30 lbs, and still going!
My pem Henry is a really picky eater too, and the best thing I've found it to mix some warm water in the kibble and let him have it for 20 minutes. If he doesn't eat it, I pick it up. Eventually they figure it out, a healthy dog won't let himself starve. Henry is still by no means an enthusiastic eater but he's much better than he used to be.