At one point AT&T was required to allow consumers to buy and connect their own handsets rather than only allowing them to rent from AT&T. Isn't that similar?
No, what you described was a simple change in how the product was distributed. Forcing Apple to engineer a way to add 3rd party app stores on their platform would require significant engineering effort from them and changing their operating system internals significantly.
So to stick with the telecom example, if you want to sell telecom equipment or operate a phone company you must include intercept capability for law enforcement. That involves engineering changes in the hardware and software, business operations changes to manage and execute the intercept requests, etc... Is that a closer example?
For Apple it might be less expensive to just make a single policy change - allow apps to use alternate payment providers. That feels somewhat close to forcing AT&T to allow alternate telephone providers.
Sure, but that's not new. Here in our EU country, governmennt dictates the railroad owner to allow other railroad companies to drive freight on it (although it fought tooth and nails to continue fleecing everyone by noncompetitive prices).
Competition is the basis of functional free market - and forces which prevent it are driving it to be abusive and not force of progress anymore.
