Good read on Pea Fiber here, it's an insoluble fiber, so it will add bulk to the stool & help the food pass through the stomach & intestines. Wonder why they need this? It's a highly processed food & it needs help getting digested.
Another Pet Food Filler Ingredient Revealed: Pea Fiber
Talks about tapioca here, it's essentially a binder/filler. It's in some grain free kibbles to help bind it. It's not considered good bc it's high up on the ingredient list, so there's a significant amount in the food.
Raw Kibble: Is This Pet Food Good for Your Pets?
Since Earthborn gives out samples, I would try it & see how Galen does on it. If he does well (nice firm poopies is a way to tell), that's all that matters. The above 2 ingredients will not hurt him. There's going to be something in EVERY kibble that's not nutritious for a dog or cat...there's no perfect kibble. You can supplement by giving canned food or fresh veggies (slightly blanched & blended is best), boiled/cooked chicken or salmon, etc. all w/no additional seasonings. Help put some moisture into his diet & a little more protein bc actual protein coming from a meat source is much much less.