What Apple did was clock down the CPU of iPhones with degraded batteries in order to reduce peak load which would otherwise result in crashes that would have made the device borderline unusable below some charge percentage.
Yes, they should have shipped the feature off by default and with a toggle, but the feature itself was amazing as it let already old phones last longer than they otherwise would have.
Apple deserves a lot of shit for their bullshit surrounding replacement parts, but this particular topic is something they get an undeserved amount of shit for in my opinion.