I'm not saying you "must" go to PADI to learn to wreck dive. But most of us aren't born a wreck diver. It's a fool who says he can't learn anything from a course, no matter how poor the course might be. Heck, I even learned something from the PADI "Boat Diver" course.
I've been diving for 25 years now, have dived most all the wrecks within recreational limits in NC, never taken a wreck diver course. Like you, I'm pretty confident I can do it without dying. But I will say I bet there's something in PADI's wreck diver course I would learn, that I don't know, that would make me a better/safer wreck diver.
"
experientia stultorum magistra" ~ Experience is the teacher of fools.