I was talking about 9.7-inch iPads. Not one is good. The best iPads like the 9.7-inch iPad Pro and the 6th-gen iPad are poor when updated. (Especially in terms of battery life).I agree on everything except "Update them and they result in an awful experience". M-series iPads have so much headroom that their performance won't be affected in any noticeable way by updates. Stand-by time took a big hit after iOS 11 and to a lesser extent with iPadOS, but has remained stable over the past updates. I don't expect it to worsen significantly with updates, it could even get better since it depends on what happens in the background. So what you said can apply to older devices that came before iPadOS but doesn't seem to apply to newer ones.
For M series, let’s wait to see battery life at the end of their lifespan. I’m a little more hopeful about performance, but we’ll see.
Apple’s entire history is one and the same. Perhaps in terms of battery life, perhaps in terms of both. Every single iOS device that has been discontinued in terms of iOS updates has been obliterated. Before being hopeful, they have to show me they can do it.