I reckon this is an unrealistic expectation for older iPad generations. It wasn't until the A8 that raw processing performance could match up to a lowly x86 Atom. Android and iOS may be more efficient compared to desktop OSes but when you start adding desktop-like features such as background multitasking, etc, then something's got to give. Only way you'll get 5 years use out of older iPads is if you never update the firmware or at least limit them. Mind, I have two iPad 4's still running iOS 6 and they're just as fast and smooth as when I first bought them.
😀
While x86 performance has mostly plateaud, ARM is still benefitting from Moore's Law. New features introduced with major firmware updates optimized for new hardware are bound to take a toll on performance, particularly on older hardware with just 25-50% the processing power of the latest model.
AnandTech - iPad Pro 9.7 vs iPad Air
I've owned iPhones since the original and useful life pre-A6 was just 1-2 years (at least if you want decent performance on latest firmware) and they're even pricier than iPads (just masked by subsidies during the early days). Personally, I limited major firmware updates on my iPhones to just one (next version). The iPod Touch with limited RAM (typically half the iPhone's), I kept on launch firmware (with updates to minor point releases).
I know the iPad 2 has often been touted as the longevity model but in reality, you wouldn't want to use it past iOS 7. That's just what, 3 years (2011-2014) of service life?
The iPad 4, I found, worked perfectly adequately up to at least iOS 9 so that's at least 4 years (2012-2016) service life. I already gave away the iPad 4 I kept updated and plan on keeping the ones I still have on iOS 6 so I haven't tested iOS 10 performance on the iPad 4.
The iPad Air, aside from more frequent tab refreshes, handled iOS 9 even better than the iPad 4 so that's at least 3 years (2013-2016) service life. I'm still undecided whether to update to iOS 10. I reckon the Air will probably handle it well enough. It's just additional restrictions on iOS 10 (e.g. no screenshots on Netflix) that has kept me from updating.