> I’m arguing for the tax because it provides a strong incentive for app developers to stick to Apples payment systems, that’s good for me as an end user.
You as an end user are not party to the agreement that Apple has with the developers. You are of course free to choose not to do business with parties that do not support Apples payment system, but the same goes for Stripe, PayPal, Adyen and all the other PSPs.
> I’m also arguing for the tax because I believe that Apple has the absolute right to collect such a tax, why wouldn’t they?
Because they are abusing their position to do so.
> They’re far from being a monopolist.
Your understanding of what constitutes a de-facto monopoly is broken.
> Stockholm syndrome?
> Mobile app development sounds like the last thing I’d want to have anything to do with.
That is your choice and your right, but plenty of high performance and/or low level applications have no choice but to go native.