With how power efficient iPhones are getting, battery degradation is becoming less and less of an issue
After I broke my 6s last year, I picked up a used iPhone 8 which had 95% battery health at the time of the purchase, and right now it’s at 89% health.
This February, had my 6s replaced with a new unit that came with 100% battery health, and recently I simultaneously ran a battery drain test on both, with airplane mode on, the same brightness level and no apps running in the background.
After 2 hours, I was surprised that my iPhone 8 with 11% less battery health still outdid my 6s, even though the 11% reduction brought the battery capacity down to about 1620mAh, which is 100mAh less than my pristine 6s battery.
As such, I’m not really concerned with battery degradation on newer iPhones. The newer, more power efficient processors are making batteries last longer even degraded, so I’m not too worried, and neither should you be. Batteries will inevitably age and lose their abilities to hold charges, and that’s to be expected. But as phones evolve with more power efficient processors, batteries can last longer.