I have the 2016 7 Plus with A10 and 3 GB RAM, and iOS 14 runs VERY well on it. In iOS 13 I have only rarely noticed lag, which I suspect is memory related, but I emphasize "rarely". I haven't really noticed any lag in iOS 14 yet, but that's because I've only had iOS 14 on it for half a day. Otherwise overall, iOS 14 feels like iOS 13.7 did in terms of performance.
So, despite this phone being 4 years old now, I don't really have a good reason to upgrade, at least in terms of SoC performance. It would be more than fine performance-wise for at least another year and probably significantly longer. Battery is still OK too, at 88%. (The battery was replaced in 2018 under Apple's battery replacement program that year.)
That said, I will likely upgrade anyway, since I have a lot of gift card cash burning a hole in my Apple Wallet, and because I want a new camera. Plus, my daughter wants my 7 Plus to use as a glorified iPod touch.
My wife has the 2018 XR (A12 and 3 GB RAM) and she won't be upgrading either for 2 years or possibly more. She has never once complained about its performance.