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.