The issue prior to that fix was that the phones shut down mid day due to running out of battery. Lowering performance on a phone with batteries degraded to the 80% level or worse in order to not have it shut down before the end of the day makes sense.

When the feedback you're getting is that people are complaining that their phones are shutting down and you then task some engineers to fix that, you get a fix. Apple said early on that it was a small number and it probably was, but lithium batteries have somewhere between 500 and 2000 charge cycles before they degrade to that level so over time more and more of the older phones would start falling into that mode.

But the accusations early on were "you're making my phone worse to force me to buy a new one" which wasn't the case. From an engineering perspective the change made the useful life of the phone longer (fixing the battery life issues).