I upgrade my iPhones too often for it to be an issue with them, but with my iPad 2, the constant reloading of apps and Safari tabs became FAR more annoying than the speed when the device got old, meaning the amount of RAM was the issue, not the processor.
Apple has been putting 2 GB of RAM in iPads since the Air 2 in 2014, and they are still sticking with that amount 4 YEARS LATER? The Air 2 processor may prove to be the bottleneck before its amount of RAM (maybe), but I just don’t see how the RAM in the 2018 iPad isn’t going to make it a crap experience long before the processor does. I bet the iPad 2018 is one of the last iOS devices to ship with 2 GB. I maintain that it’s a terrible time to buy a 2 GB iPad, especially if you want to get 4-5 years of use out of it. If you just want to use it for a year or two and then upgrade, I can see that, but I don’t.