> supported devices are fast enough now that it really doesn't slow them down anymore

That happens to be true now because Apple has dropped support for many iPad models with iOS 10, accounting for up to a third of all iPads in use.

Running iOS 9 on the iPad 2, 3, and iPad mini was frustrating. This was only three months ago, so I wouldn't rule it out for the future yet.

But even if Apple may be better than most android manufacturers, Apple still doesn't support devices it considers "Obsolete"...and there is nothing you can do about it other than buy a new phone since the bootloader is locked down. According to https://en.wikipedia.org/wiki/List_of_iOS_devices anything before iPhone 5 is considered "Oboslete" and they don't seem to be releasing updates. On the other hand, I've been happily using my Samsung S3 which cyanogenmod has been pushing latest android updates to nightly...and that is likely to continue as long as there are enough of us who care, even if cyanogen and samsung goes away.