> trivial to not buy Apple products
Irrelevant. Monopoly doesn't mean coercing people into the market.
> easy to make alternatives to Apple products and easy to buy feature equivalent devices to Apple products
It's not only not easy, it's not possible. Your mistake is thinking of phones as computers. They are not computers, at least not to the vast majority of users. They are devices that connect to other compatible devices to do telecommunications. It's just like if plain old telephones ran a proprietary protocol and only one vendor could make them.