I see you writing multiple things, including
- newer iOS versions are less efficient on older devices/leverage more compute from devices
- people can fixate on min/maxing their battery longevity and stats
I'm not going to dispute #1. I don't know if it's true, but it wouldn't surprise me if it were true. It is the nature of the space though. If Apple is going to increase computing power and usually efficiency on newer devices, which seems like the thing to do, it will have consequences for better or worse on older devices (new features, harder hits on battery for older devices).
As for #2, I won't argue there are some that have expectations on battery longevity and health that are out of whack. However, <80% battery capacity on the current generations of Li batteries is end-of-life, per the manufacturers. To me, that doesn't mean if falls off a cliff for functionality, but it certainly means the discharge curve often gets off-spec. Unexpected voltage and current delivery can and does start happening, and that's not great for experiences with electronics. Personally, it's not a big deal to replace them at that point, so I do without a lot of drama, and keep my expectations reasonable. I just don't see the reason for your passionate response to others replacing their batteries at their end-of-life (with full acknowledgement that those batteries still function, just in a degraded state).