Where you're pretty much stuck google play store, which has also banned the app...

There is side-loading, but there's a lot of friction there that I wouldn't expect normal users to withstand.

Its a monopoly for developers. As a company you can not not use the app store because half of your customers are there and very few companies can afford to give up half of their customers.

Developers can chose to target other platforms.

There are countries with 0% iOS market share, half of zero is still zero.

I personally don't like Apple and will never buy an Apple product, but I fully agree. People who buy Apple products are perfectly fine with the way Apple restricts their platform. If you don't like this as a developer, then just leave and stop developing for iOS.

A single big company doing this just to cut down on some fees just reeks of greed.

It is not a single company, Google also kicked Fortnite, and it has been a thing in game consoles, car infotaiment systems, pre loaded apps on TV settop boxes and blue-ray players,....

The world is unfair, no one is expected to do charity for developers.

We are not a special snowflake job that isn't expected to give others the necessary payments to keep the whole chain working.

For most business that is not a choice. If you are making a utility or game then maybe, but can a company like uber decide that they will only be available to android users?