I have an amazing iPhone X and an iPad Air 2 on iOS 11 that still runs great. Both devices perform exactly as I expect- the iPhone X is smooth as butter and the Air 2 is surprisingly responsive for a device that's three generations behind.
I hope Apple will begin to inform users if their devices have batteries that no longer handle intense power loads, but it's not some huge conspiracy like some make it out to be.
Eh. I replace my phones every three years, so end-of-life phone (to me), no issue with software throttling my device if the battery is in sad shape. Not that I tax the phone that much (read: play games), so, rather have the software stretch the battery life vs gonads to the wall performance for making calls, email, web, podcasts and a dead battery after only a few hours.