Considering the tight integration of the OS and the hardware, I would offer the comparison that it's more like a CPU not allowing any code that's not signed by Intel to run. Or, more aptly, only allowing one specific OS to run on their CPU and that OS has a restrictive policy on application usage.

Sure, you could go with AMD but does having other choices excuse a company? It certainly violates the spirit of anti-trust laws. Apple makes and controls 46% of all the mobile devices in the US. The nearest competitor is Samsung, who makes 25%.

If Apple allowed other OS's to operate on their phone, then they could say "If you don't like our integrated app store policies and policy of not allowing other app stores, use a different OS". But until they do that, the OS and the hardware have to be seen as one thing.

Apple makes and controls 46% of all the mobile devices in the US because their methodology for designing, building, distributing and iterating on the product is successful. Consumer satisfaction, retention and growth are bi-products of this success. Apple doesn't play mean tricks to gain market share. They simply build great products, invest more in innovation (CPUs) to continue making great products. The m1 chip shows this. You can't pick apart what Apple does and give it some attribute/feature of an ecosystem model. Right now the market is Apple vs. ecosystem. Consumers have choice to buy from Apple, or buy from an ecosystem. We should focus less on trying to handicap Apple and start figuring out how a leader in the ecosystem can rise above it to compete with Apple head on.

It's not so simple. Because Apple hardware and software are closely interwoven it's hard to change to another brand. Most of the software and accessories only works with Apple hardware and software so if you change you have to make rather large expenses to keep the previous status quo. I.e. even if you are unhappy, for some it is simply too expensive to switch to another brand.

But this is true for the game console market in the comment I originally replied to. When you buy a game you are locked in, you can't put your Halo disk in a playstation or transfer your Nintendo store purchases to Xbox. If you have an Xbox and all your friends load up on Playstation, its going to be a significant cost to get the new console and library you want to play multiplayer with them. For some reason people care more now that its a phone than a game console.