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.