It should also be noted that Apple admitted at one point to purposefully slowing down older iPhones too, which very clearly was done to get people to upgrade. If that’s not planned obsolescence I don’t know what is.

It is the literal exact opposite of planned obsolescence. Apple introduced a new feature, still present in all of their phones, to extend the useful life of old phones. Batteries degrade with time and use and, after a certain extent, are not able to maintain the sufficient and stable current levels for a phone to operate, particularly during moments of peak power draw. If this happens (and this applies to every Android phone as well), the phone will just shut itself down. Specifically it will shut down right in the middle of you trying to actually do something, since that’s what’s going to cause a spike in power demand. Apple added additional power management to iOS to dynamically throttle power use only when and to the extent needed. On a phone with a perfectly healthy battery, it’s not in use at all. On a phone that’s had years of hard use, it might still only barely be noticeable with some high-demand tasks running slightly slower or the screen slightly dimming. The worse health the battery is in, the lower its current charge level, and the greater the temporary spike in usage, the greater the throttling. Recharge it or resume less intense use and the throttling stops.

So after release (unplanned), they gave new life to what were otherwise obsolete batteries so you could wait longer to upgrade.