They can't charge a cut of revenue unless they monopolize payment processing, so if as you say they start charging for developer tools, if they charge too much of a flat rate for those, many developers will rightfully walk away, so no, they can't make obscene profits like they're doing now without controlling all payments in iOS apps.
There's a bunch of reasons why it'd be a PITA for everyone involved if they were forced to do this, but no matter what happens the revenue sharing is never going to go away as long as Apple wants to keep that business model. All the frictional costs (more lawyers and accountants) to verify they collect the right royalties is exactly why courts are ultimately going to side with Apple, because the current system is the ideal one for all parties.
Developers have been so steeped in propaganda about "payment processing" that they have no idea what the 30% commission is for.
A court or regulator could force Apple to allow third-party payment processing, side-loading, and third-party app stores, and Apple could change their business model to directly charge for the tools and the SDKs that every developer uses to make native apps. The only way to avoid those costs is the way that already exists today: make a web app.
Right now the payment processing costs have been integrated into the commission, but they could charge whatever the market could bear to license their IP for a royalty, so in effect developers could end up paying more.
There's nothing in law that says Apple can't charge money for their software. That the use of developer tools and SDKs were free on other platforms like the Mac doesn't mean that it's legally required that it be given away for free.