Even given that, I don’t see how “end users must be able to change batteries in a practical way” would not negatively impact the quality of the iPhone I’m holding in my hand right now.
From a water-resistance standpoint alone, I think my phone would suffer in at least one dimension that matters to me. (It’s an Xs Max and yes, I bought used, confident that the water resistance was intact. If I sold it now, the next buyer has that same assurance.) Phones get wet at some low (but not insignificant) rate; it’s hard to avoid that across the entire population.
What you're describing, and I agree with you, is what many legal right to repair advocates are fighting for.
However you'll see many people conflate it with easy to repair and easy to get parts, or repair without voiding warranty. Which IMHO should be separate talking points, but alas, they're all jumbled up when these discussions happen.
It's also why I don't think right to repair will please most people. Because the scenarios you described are limited and outside what most people are thinking e.g home repairs of cell phones
NEC Medias smartphone from 2011, removable battery and IPX7 which is waterproof up to 1m deep. It is 8.2mm thick.
The Iphone 4S was released that year @ 9.3mm thick.
It is possible to make phones that do it, the companies don't want to.
Reasons many devices are not repairable include: DRM built into parts to prevent replacements, no repair manuals (see Thinkpads compared to macbooks). Also measures to prevent people from flashing the firmware or updating the software once a company decides to drop support despite the hardware being still functional, or easy to put back up to speed by changing a battery.
Forcing companies to stop these anti-consumer strategies has 0 impact on the designs while making electronics far more repairable.
I find the "right to repair will make my devices big and ugly and appeasing to the evil tinkerers and hackers" angle really dishonest.