Interesting that this effect may be a byproduct of automatic scaling the CPU frequency based on remaining battery capacity, rather than the newer OS versions being purposefully poorly optimized (like most people assume)
But you aren't reporting the phone being warm to the touch, so... hm.
Have you tried wiping and restoring it?
It could be interesting to back it up, wipe it (and maybe remove the SIM card for completeness?), install the worst performing apps on the fresh install, and _then_ (maybe wipe again(?), then) restore it back to normal.
If app performance is terrible in the fully-wiped state, I'd take the phone into an apple store (regardless of warranty status) just to see what they say.
Hmm. Just thought of this: maybe your battery is like the OP's from reddit but in really bad condition, and your phone is downclocking itself to compensate?
Adding this to my comment because it's relevant
I would get your battery checked out for a start. Many of us (including myself) have iPhone 6s and seen no major issues.
basically there are times when it will drop sigbnificantly in a short period, but i have also had it last significantly at 1% and go from ten to 1 in a second - then i rush to plug it in and as soon as I plug in the cablee it immediately jumps back to ~15%
so I think its both hardware and software...
If so, I’m in for a try.
I prefer to skip even the backup step, instead relying on cloud sync for contacts etc, and manually dumping a couple apps.
After doing a full backup using iTunes, then resetting the phone to factory conditions, and finally restoring the iTunes backup -- my storage space returned to normal, and the speed increased dramatically.
I suspect that over time, internal files accumulate (e.g. log files & upgrade restoration points), and this accumulated cruft gradually consumes space & degrades performance.
Now, if you use crappy 50-cent third-party chargers, I don't know what happens.
I have a ton of lag on my 6 on iOS 11. I bought it roughly 3 years ago
I'm light on battery though. No movies, no books, a wee of games, some browsing. Heaviest use is sports tracker and maps. I do use it for testing apps nearly daily. But usually it's hooked up to Xcode.
If you're on the fence on whether you should upgrade from an iPhone 6 or lower definitely stay away.
I seem to recall the first several years—maybe even the first decade—of OS X being marked by each new release being faster on the same hardware, though dropping support for the oldest hardware. It was definitely true for the first few releases of OX X, because 10.0 was notoriously sluggish. I also don't recall any slowdowns with my 2006 iMac across the several upgrades it received before Apple made 64-bit firmware a hard requirement.
If there's any truth to the meme you cite, it probably stems from the mobile side of things, where iOS started out fairly efficient but the hardware was very underpowered. (And in that case, I'd like to point out that the iPhone is only 10.5 years old.)
It’s very real though. A fresh clean reset of my old iPhone 7 had a significantly lower Geekbench score, and that went away after the battery (capacity: 78% of design) was replaced.
I was preparing to do a backup, wipe and restore (which made my first gen iPad Retina somewhat usable again) but first thought I’d try some of the tips online for speeding up iPads, and to my surprise it really worked and made it much more responsive.
If I remember correctly, the ones that seemed to make the most difference were: disabling animations (in accessibility) and disabling any kind of notifications/background app refresh/auto update, but if you’re in a similar situation it’s certainly worth trying some of the other tips in guides like https://www.macworld.co.uk/how-to/ipad/how-speed-up-slow-ipa... and if that doesn’t help, doing a backup and restore.
1. If such a common complaint has such a simple fix, why isn't Apple shouting this information from the rooftops? Why do we need anecdotal information posted on Reddit to figure this one out ten years after the launch of the first iPhone?
2. Being a byproduct of automatic scaling or the commonly cited flash degradation doesn't explain the abrupt spikes in the search for "iPhone slow" around the release of a new iPhone (Google Trends: https://trends.google.com/trends/explore?date=all&q=iphone%2...). Could it be a purely subjective, psychological effect? Does anyone have actual benchmark data on this?
People would not notice drastic performance issues after doing an iOS upgrade if it was just the battery.