The notion that you have that I need to justify or prove anything to you says it all. Good luck in life.I don't really care what you do, but I do find it interesting in how you make your choices, that's all. Also, you chose to make an account on a public board and state your opinions. I'm just challenging you to back them up. I might learn something from you, though that is seeming to be not the case right now. You aren't even obligated to respond to me. Don't take it personally - I am disagreeing with your preconceived notions and assertions of fact, not with you as a person.
There is absolutely a shelf life on training. There is an old saying that practice makes perfect, but that is not true. Practicing something wrong may make one an expert at doing something the wrong way. Perfect practice makes perfect is the correct phrase.
In your case, it seems like you're set on justifying every way that has led you into your current setup, but not considering the others. Maybe you have done so and just haven't made it clear. Regardless, you should go try some real, formal training with a shotgun in close quarters.
Have you ever taken a force on force class where people are shooting back at you?