Reddit users explained that was because Apple, with iOS 10.2.1, dynamically lowered the maximum clock speed of the processor.
To recap, the iPhone 6s was suffering through an unexpected shutdown issue a year ago, prompting Apple to release a fix in iOS 10.2.1 which solved the problem for most.
Popular bench-marking platform Geekbench issued a report investigating the claims by iPhone users that each new update slows their device down. Last week, a Reddit user whose iPhone 6s had been slowing down found it received a massive performance boost when they replaced the battery, leading to an extensive thread on the subject. The problem he found was that iPhones were slowing down as their battery life decreased, and the issue was widespread enough to affect even the iPhone 7. The reason for the drop in performance is the degrading battery. This drawback will definitely hurt Apple's more affordable offerings in the country, as the SE doesn't necessarily suit the needs of the average Indian smartphone user.
All that said, there's reason to believe that Apple will report a blowout quarter next month. This did not change whether I had low power mode on or off. "Nope. 2526 Single and 4456 Multi".
Apple told Business Insider at the time that "the diagnostic data we've received from upgraders shows that for this small percentage of users experiencing the issue, we're seeing a more than 80% reduction in iPhone 6s and over 70% reduction on iPhone 6 of devices unexpectedly shutting down". Particularly an older battery. The data from Geekbench indicates that there is more than one reduced performance state. This translates into a slower performance without any notification creating an "unexpected" third state which is created to mask the low battery power. Further restricting phones like the iPhone X to an incredibly small percentage of smartphone users may make business hard for Apple in such a large market that they continue to struggle to break into.
"This will likely feed into the "planned obsolescence" narrative". We have reached out to Apple for comment, and we'll let know you if/when we hear back.