You might see antitrust law force Apple to allow sideloading, including apps built by toolchains third parties have hacked together.
You're also not required to use a Macbook; the Mini is $500.
If a monopoly is allowed to choose, it can use its domination in one vertical to influence another vertical.
Anyway, I would prefer a Linux version of the iPhone SDK. I do not use neither Windows nor OSX normally.
If you don't like the MacBook, you can buy a Mac mini and use it as a build server from other (non-Macintosh!) computers. There are tools for other platforms, and Apple isn't obligated to maintain their platform for "non-standard" use. It's not antitrust, and it's not a technicality. They're not obligated to open their platform, because they're not restricting something that was previously open.
I don't like it either. That doesn't mean it's illegal.
Big Tech also formed a cartel to lower engineers salaries. This is also something that should be punished by law (and AFAIK, they did win a class action suit).
I do think this is a problem and needs to be addressed.