Another cat diet question, cat has chronic loose stools / diarrhea

Me and my girlfriend have two cats, a 3 y-o male and 4 y-o female. We moved in May, and again in August. Ever since the first move, the boy's poop started getting looser and smellier. We have always fed the cats Purina Naturals dry cat food. We took the boy to the vet, poop and blood tests revealed nothing, but they prescribed something anyway, I think metronidazole, which had no effect. All throughout this time, he's showed no other differences in health. He's very active, friendly, playful, eats plenty, drinks plenty, and is not dehydrated based on the scruff test.

Knowing little about proper cat food, we tried switching to generic wet food, which made his poo basically liquid. Then we somehow decided upon Hill's Science Diet Sensitive Stomach dry food, and he showed a lot of improvement. His poop is definitely not optimal, but it's way better than it was this summer. Interestingly, he used to eat all of his food as fast as he could. Immediately upon switching to Hill's, he's become a grazer.

I've been poking around this subreddit for a bit and noticed that people generally recommend against Hill's Science Diet. I looked at the ingredient list and the top ingredients are brewer's rice and corn gluten meal, which from what I've learned are not exactly what cats should be eating.

Has anyone had much experience with cats with diarrhea? The ingredient list for Blue Buffalo food seems pretty good but I don't want to switch foods and have my cat start pooping liquid again. Any thoughts?