This is why Android isn't really Open Source in spirit. It is as closed as Apple is.
Hardly. Even on a non-rooted device all you have to do is tick "Allow untrusted sources" in the settings and then you can install stuff outside of Play Market as much as you like. Play Market is closed, yes, but it's also a separate thing and not required for using an Android-device. iPhones and iPads and the likes, as far as I know, require doing a lot more than just ticking a single box to allow installation of things from outside of Apple's AppStore.