No it's not, because you could previously self publish apps for any major os and not be locked out by default from virtually all devices. I understand the benefits of an app store and walled garden (not that I want one for myself, but I understand), it's always been way too much nonetheless.

That's still the case for computers.

But before the iOS app store, there was none.

Before the App Store I sold software on my web page and the only fees were the 5% PayPal takes and $9/mo for dreamhost

You can still do that.

You can't side load on iOS.

Yeah but you access the same exact markets as the old days, just maybe not the new ones.

What changed though? Before iOS and iPhones existed, you also couldn’t sideload on iOS, but no one was complaining. Apple created a new product essentially from scratch, and it has some limitations to how software can be distributed to it. Your car infotainment center and your fancy air purifier probably also don’t provide an easy way to install arbitrary software on them. But creating a new device that can’t do every conceivable task doesn’t change how you can sell other software online.

Mobile is now the main computing platform for many people around the world[0]. It’s no longer a toy for yuppies or a console device. It’s time the platform grew up from being as limited as a car infotainment system.

[0] Today roughly one-in-five American adults are “smartphone-only” internet users https://www.pewresearch.org/internet/fact-sheet/mobile/

Nearly three quarters of the world will use just their smartphones to access the internet by 2025 https://www.cnbc.com/2019/01/24/smartphones-72percent-of-peo...

For a mobile platform?

If you mean for desktop, nothing has changed.