I'm really not. I have apps on my iOS devices right now that I didn't get from the app store; all I had to do was download them from the publisher, and then accept their signature in the security settings. (In my case, it's the frozen-in-amber old version of Sonos, which they'll let you have if you ask for it, but presumably this would work for anything.)

Anyway, you're coming at me apparently ready to argue about whether it is or isn't a walled garden. That isn't what I'm asking about. I'm asking what, specifically, Apple won't let you do that you want or need to do that leads you to describe it as a walled garden.