So what is the need here? Who isn't able to access something they need access to and how is forcing Apple to open up their hardware and software platform the correct solution to that problem? And I'm asking honestly here, are there any actual necessary services that are only available on iOS? Not more convenient on iOS, unavailable anywhere else. If we accept the arguments against iOS at face value, it seems impossible for there to even be any necessary services that are more convenient on iOS. The major arguments are Apple is too restrictive, they prevent apps from doing things, they prevent PWAs from working, they disallow integrations that developers want. By all accounts, the iOS experience should be measurably worse for users in every single way for any 3rd party service. If removing Apple's restrictions was important to consumers, if it was actually harming them in ways that they didn't think was worth the benefits those same restrictions provide, Android should be mopping the floor with Apple. But they're not. And none of the arguments I've heard for regulating Apple have been because of failures of iOS users to be able to access critical government and economic resources.
The closest arguments that could be made are about things like blocking access to certain VPNs or other "subversive" applications in places like China and Russia. But of course, the proper way to regulate that would be to mandate wide open consumer access to strong end to end encryption that governments can not control or have access to. But mandating that sort of thing would be admitting that even "western" governments are untrustworthy and might need to be subverted. It would be mandating access to law breaking tools, which the EU and the US are not eager to do even here, let alone eager to step into that political battle on the world stage.
The argument is simply; the smartphone is the platform we have chosen because it makes our lives so much better. It does its job so well that it has become a critical part of the economic and social fabric of the country. Thus we need to make sure it's regulated (up to a point, obviously) so that the public's needs and that of the larger economy are met, while still maintaining the financial incentive for smartphone platforms to innovate.
Consider; it's possible to walk to work/banks/government offices for the majority of people but vehicles are convenient and time-efficient so that's what people choose. Accordingly, society accommodates and regulates vehicle use. Same thing for radio and television in the past... it was possible to get information and entertainment elsewhere, but people chose those mediums because they were better than the alternatives. It's because of the popularity of cars/radio/television that those things deserved regulation, nothing else.