I don't know why you're upset. If all he said was that canned food has no real advantage over dry, that's surely basically true, especially when your animal is healthy, does not have diabetes, has all its teeth, etc.
I've had many cats and dogs in my 49 years. I've used both dry and wet foods off and on. Usually, without buying ultra cheap, mind you, it was a matter of two factors: what the animal would eat, and what I was willing to pay for the food.
For instance, I had one cat who only ate Meow Mix her entire life. She hated anything else with a passion, and acted purely addicted to her Meow Mix. She loved it dearly.
I had a precious little Chihuahua that was rather finicky, and I had about two or three different brands of soft canned food she would eat, but invariably, despite having different flavors even in one brand, she would tire of one, and not eat for days on end until I'd rotate to one of the other brands. As she aged, and got fat, I decided to force her on dry food, and measure it. She spent her last few years lean, perfect weight, and very healthy, albeit clearly thinking I was insane to make her "work so hard" for her food (to have to crunch and chew it that much).
I agree that when a dog is diabetic their feeding takes on precision and you cannot simply use any old food. I'm only referring to healthy animals, with, as I already stated, all their teeth.