I realize that your post is quite old, but I am just getting back to reading The Forum again.
What gives meatloaf that meaty flavor is fat and umami. I hope I spelled that correctly. When using 93% hamburger you are getting rid of all of the flavor. Using a higher fat content in meatloaf, like 83%, you are putting in more flavor. You can get rid of the fat when it is baking by putting it on a rack to drain the fat as it cooks.
Additionally, mushrooms have a lot of umami flavor. I like Ina Garten's mushroom turkey recipe.
https://www.foodnetwork.com/recipes/...eatloaf-recipe
It makes a big meatloaf, but you can freeze it. My husband, who is a very picky eater, doesn't even realize that it is not made with hamburger. Of course, I would never tell him. The meatloaf is quite flavorful.
By the way, Trader Joes had a seasoning called MULTIPURPOSE UMAMI SEASONING BLEND.