Zignature is a good choice as it has a selection of proteins and none of the common allergens. I also like Farmina. Best rule of thumb is stay away from the big companies like Mars, Nestle, Purina. You will be surprised what dog foods they manufacture! Always check who the manufacturer is to be...
Don't beat yourself up. Years ago, we had a 4 year old rescue greyhound and was given an 8 week old American bulldog. Everything was great until the AB turned 2 and she decided she wanted to be alpha. I have no idea what triggered the first fight, but it was horrendous. Side tables turned...
I would have a vet check him out. It is not normal to breathe that heavily unless he is hot, and as we all know, EBs cannot tolerate the heat, so that would be another concern. Good luck.
When I got Buster he was a bit overweight. The vet had me cut his food down (Zignature) to 1/3 cup with green beans topper, twice a day. The weight came off slowly but surely. He was 6.5 years old and had low energy. He also got the occasional egg or chicken livers.
Sorry, can't help you there but welcome to the forum! If my dogs would be anything to go by it would have to be pretty substantial! I have a feeling they would have tried to change the timing!
If anyone follows BulldogPabs on FB, he used Oodles for his dogs but recently changed to another food. It is called Majors Banquet.
https://majorsbanquet.co.uk/