I think if you're going for a classic burger you need to keep it simple, salt. pepper and maybe a wee splash of Worcestershire, no binder or grains or anything else, as someone mentioned then you've got meatloaf. If you have the tools, grind the meat yourself, I know that sounds like a huge pain in the ass but it's really not( make extra and freeze it) .The onion, tomato etc should all be added on extra to every individual taste.
I just built a restaurant nearby and got to be taste tester for most of the new menu, they dunk the whole burger in a mix of soy sauce, hot sauce, seasonings etc and then put it right on the grill...give it a try