It has been anti-confirmed by me. My iPhone 6S continues running at 50% CPU speed, even when charging from the OEM adapter. Only thing that makes it run (a little bit) faster is if the battery charge gets above 97%.
(Also worth noting that the battery in my phone still holds 87% original capacity.)
That this is happening when the cell is still at 87% capacity is really the problem here. How do you justify degrading your system's performance when the cell is still soundly in the healthy region?
What threshold(s) are used by Apple to determine when to throttle?
If a new battery is purchased today, how many months of daily usage will cause Apple throttling to begin?
If a Samsung and Apple phone are purchased on the same day, used the same amount and benchmarked each day for 24 months, would their performance graphs look similar?
Regardless of what chemistry they are using, a lithium cell should be capable of producing more than enough power for a cellphone at any residual capacity before it becomes useless. You aren't discharging at more than 0.5C on a portable device.
(Also worth noting that the battery in my phone still holds 87% original capacity.)