The fact that phones have no option to bypass the battery when plugged in is another obvious decision to kill batteries on purpose. In fact, I built a relay that connects to home assistant to turn off my charger when the phone reaches 80% at night. My battery is much healthier for it. It would be dirt simple to add this option to your phone OS.
As pointed out by sibling comments this is somewhat common nowadays. iPhones will IIRC default only charge to ~80% overnight, stay there, and only charge up to 100% when it thinks your normal wake time is approaching. I remember Macbooks starting to do this at least 10-15 years ago. I'm not sure well this aligns as "an obvious decision to kill batteries on purpose". Is it possible that it isn't a grand conspiracy, but instead a natural consequence of having to quality and expense of parts vs what one thinks the market can support?
The other option from your proposal of course is never to charge above 80%, or call 80% "100%", in which scenario you would almost certainly have the same sources accusing them of being underhanded and anti-consumer by "artificially limiting battery capacity".
I see batter limiters in MacOS, Samsung phones, Framework laptops, Microsoft Surface devices. Now we just need to normalize it on budget devices.
They may well had a technical reason, but I certainly don't appreciate them being underhanded about it. I don't have an apple device right now, so I'm generally out of the loop, but it seems like right now people can toggle the slow down, and also go get their batteries replaced. That seems like a pretty good end situation. Did I get that right?
Much like the iPhone 4 reception fiasco. Nothing actually changed reception-wise, except they changed the way they calculated and displayed the signal. But people were now seeing _different_ signal profiles than they expected, and apparently Apple decided (eventually) that changing it back and giving everyone a free case was better marketing that continuing to try and persuade people of that.
If we repeat this lie long enough we might believe it ourselves!