This is not quite true. If you write your own app you can install it on your iOS device. If someone put an iOS app on, say, Github, you could easily install it. No need for the App Store or Apple's review process. An app does not need to be signed unless you want to submit it to the App Store. Also, you can install iOS without using the App Store if you have a developer account.
I'm not disagreeing with you that iOS is far less open than Android.
That's not quite true either. Because an app installed like this will only function for a very limited time (a few weeks i believe) and then it expires and you can no longer start it. This means it is not practical and NOBODY will use this: which explains why there are none/hardly any of such apps available on Github, etc.
I did this with the f.lux app in the past and it was very annoying/not usable because of the necessary "recompile frequency".
Though I guess most people may just want to throw their arms up and force the government to write a law to make such easier for free?
Haha, no. Last I did this, you must have a Macbook, you must configure Xcode, generate new certificates, sign the entire application bundle, and then you get to sideload it - and never get an update ever unless you repeat the entire process.
In contrast on Android: "This application is from an unknown source. Would you like to still install it?"
Technically you just need macOS, I don't think there's anything stopping you from doing iOS development on a hackintosh.
I'll agree that the process is pretty ridiculous in comparison to Android though.
Which automatically voids any and all warranties on the product.
Like it was mentioned above, if you want to reach Playstation's, Nintendo's, or Microsoft Xbox's regular warranty abiding customers, you HAVE to go through their marketplaces and gain their approvals and pay their license fees first
If I sell you a general desktop computer and refuse to let you install any banking app aside from Bank of Evil, then I'm probably breaking antitrust statutes.
Playstations and Nintendos are more like video poker machines. Sure, they could theoretically run a bank app, but they're sold as locked down gaming only consoles.
You can still run Android without Google Play Services, even though it's not a great experience.
Granted, there are tradeoffs. iOS is more secure in this space than Android, but Android is far more open on what you can do.
For example, Amazon created an app called Amazon Underground that would let you purchase and sideload apps onto your Android device from Amazon. Some of these apps didn't exist in the Play Store, so you had a viable option to buy exclusive titles from someone else.
On iOS, there is zero opportunity for a situation like this to occur. Everything must go through the App Store, and that's why I view it as a monopoly.