One must train differently if you are not going to use corrections. One failure you say, is that he had no recall. What does this mean? You called the dog and he wouldn't come? What happened then?
A positive trainer would not use the command unless they were able to enforce the command immediately. So if the dog is in the back yard and you want the dog in, you go and get some cheese, call his name, offer the cheese, or go out and get the dog and bring him in, but you do not command the dog to come. That TEACHES the dog to ignore you.
When the dog is on lead, you get their attention, show the treat and tell them to come, if the dog comes, then you give the treat. If the dog does not immediately start coming, you go to the dog (on lead so he isn't going anywhere else) and you bring the dog where you want the dog to be and then reward.
Positive trainers need to find what motivates a dog. I too had a dog that could care less about treats. I had to work only with praise with her because that worked for her. Other dogs will work for a tug or a special toy. Positive trainers need to be creative sometimes.
There are not that many trainers out there that use no negative markers whatsoever. For some dogs, lack of praise for an action is enough to understand that they did not do whatever right. For some dogs repeating the action again is enough. Negative markers for behavior do not have to be physical to be effective.
A good trainer should have been able to help you work with that dog without a prong. You found a trainer that helped you train the dog with a prong, that's fine. The dog got trained, and you love the dog. But that doesn't mean the dog couldn't have been trained without a prong. Some trainers could have probably screwed up training this dog with a prong.
For some dogs the prong collar can make training an easier task. And some dogs will shut down on a prong collar. Flat collars and martingales normally do not shut dogs down. It is a training collar, and a correction collar. I am not so much against them, I am against the idea that dogs will be dangerous, put down, or unmanageable without them.