There’s an easy answer here: don’t buy an iPhone. It’s not as though Apple have a monopoly on smart phones as they’re only number 4 on worldwide sales. If you want greater freedom to do what you want with your phone, buy a different brand and let those who are happy to let Apple retain control do so. If enough people desert Apple they’ll change; if, OTOH, enough people are happy to let Apple stay in control, there will still be other suppliers who don’t keep a tight rein.
This isn’t a new argument, even within ICT circles: you only license software and suppliers keep tight rein on what can be done. In fact, SaaS is reinforcing that approach. Open source is there for those who want to have more control. So with hardware, don’t buy something that doesn’t do what you want it to: you know Apple will want to maintain control so buy from someone who doesn’t. Nobody is forced to buy an iPhone.