I'm not sure how this is relevant. Throttling has been present in iOS since at least version 10 (2016), if not longer - IIRC 10 added the settings UI to override throttling if you want to, but I'm not sure when the actual capability landed.

Preventing ecosystem fragmentation is well and good, but it's orthogonal to publicizing that the OS does CPU throttling on devices with batteries whose power delivery is compromised by age, and making clear that a cheap battery replacement will do as much to solve that problem as an expensive new phone will.

(I do my own refurbs, so I can vouch from experience for a battery replacement solving throttling. There's no deliberate derating of older devices qua older devices that I can see, but it's reasonable that people believe there is, because Apple has done a terrible job of making clear what's actually going on. One of many cases where their habitual allergy to transparency has harmed them and their userbase alike; it's hard to blame kremlinologists for being kremlinologists when that's the only way to try to figure out what the hell your company is doing.)