My wife has two old iPads and an iPhone 4 and it always puzzled me that they run so slow. The Safari browser, which is naturally slow, is glacially so on the oldest iPad. I used to put it down to the software - including iOS - getting bigger and needing more memory. But this perfectly explains it.

I'm not against them doing it, but they should have been open about it. Or made it an option - speed vs time between charges.

I have old Samsung and Nexus tablets on which I can run old or limited versions of Android and they go as quickly as they did when new. You can't do anything with an old iPad.

I've noticed also that some iOS apps are not updatable on her versions of iOS (none of my wife's devices can be updated beyong iOS 9) despite the changes not requiring extra hardware. I'm suspicious that Apple encourages them to do that.