I have iphone 11 and you can have battery replaced just fine. I did it few months ago and the phone became like new. I am not sure about Apple in US but if they won't do it then some third party will.
The bigger problem is that app and web designers have stopped accommodating smaller screen sizes. I can't use my bank's app on an iPhone mini, because the buttons end up off the bottom of the screen (and the app doesn't scroll). Ditto for a number of popular web apps.
My eyes aren't great - I need three different sets of glasses: reading, office, long distance - and I'm clinging on to my 13 mini, desperately hoping that they in fact end up making something smaller. Granted, I bet I'm not the median buyer, but I would instantly upgrade to an iPhone that's around the size of the 4.
Things that we called "feature" phones nowadays and iPhone 3 worked alright with all sorts of people. Maybe phone manufacturers shouldn't opt for putting so much bullshit into the screens. Reading news, video calling people, audio calling, recording voice, messaging. They all work alright with small screen estate and good UI design.
The only thing I see a possible issue is dealing with camera features. But, you know, tech companies should actually innovate stuff... I know radical.
One could argue that a lot of 50-ish people have pro max with iphone 5-ish screen estate.
Small screens ain’t gonna happen