That argument isn't really valid because Apple FORCES you to distribute your app in their store. If you could sideload iOS apps, then Apple would have a valid argument if you wanted your app in their store.
Apple provides an iOS/iPadOS/tvOS/watchOS ecosystem. It has advantages and disadvantages. As a user, one of the advantages is that all apps are available from one secure, curated source - The App Store. That helps most users keep their devices safe. Some people do not like this (a perfectly reason position for them to take), and they can buy Android devices (or any of the other non-Apple systems). Given that Apple's market share does not exceed 50% anywhere, and in most places, does not get about 25%, they are not a monopoly and people have lots of other options.
To provide another Apple example, if Hey wanted to distribute a Mac app they'd be able to do so without having to implement in-app purchases, outside of the app store.
You are correct that Apple has different policies for their Macs, than they do for their iOS-related ecosystem. They are, however, quite different platforms, and serve different customers. Again, Apple has been very clear about these policies upfront, no one - not customers, developers or enterprises - should be surprised about these requirements.
I wish people would stop the excuse that "Apple is letting you use your store; you should compensate them for that." Apple isn't LETTING you use their store, they're FORCING you to use it just to have access to a significant portion of the market.
Nope, it is not an excuse. No one is forced to sell their apps on iOS, nor is anyone forced to buy iOS devices. There is quite a healthy market for competitors. Further, you seem to miss what a ****** user experience this would create if they allowed companies to do this. I like being able to pay via in-app purchase for items through that I only use on iOS-based systems, because it means I do not have to create a new billing relationship,
etc., while I tolerate it for services where I need access from outside that walled garden, it would make my experience worse over all if more companies did what Hey.com wants to do.
Note, I like Apple products and services. I'm just willing to call them out on stuff like this.
As I have said before, some vocal users on here what Apple to sell a different product than they do. You have every right to want that. At some point, you will have to decide whether the things you like about the ecosystem out weigh the things you do not like and decide if you want to stay. However, you (and others) should also recognize that there are a great many users who prefer things this way and do not want Apple to change these things. Having worked with a large mobile games company, I saw the difference between the iOS and Android markets. Since it was easy to side load products, they sold very few copies on Android (apps would be very quickly pirated and widely distributed). As a result, only the largest selling titles that could be ad-supported were ported to the platform.
The change you want, will invariably lead to that. At the moment, things are great. Those who do not want a curated world have a large array of options. Many of the rest of us like things as they are.