OS only works kind of ok with the device shipped on the same year (iOS11 may break this rule), it will slow down everything else.
This became part of their practices, slow down older devices, focus on new consumers. Software is garbage even on new devices. So many betas, and fixes that make evident that Apple software is garbage. Good for them (and us) to the use of digital downloads, in the past they would have been force to ship quality software in a disc, now we got use to software that is partially working, to spend the rest of the year updating it until is kind of what should be shipped since the beginning and to be part of they QA process which doesn't work because. They may talk about privacy, but in the other hand they slow down your devices so you buy a new one, that is another way to show lack of respect for consumers. And give the person who wrote the article an iPhone and then ask the person to update to iOS and keep using it, then write that article.
I have an iPad Pro 2gen, with iOS10 the performance was really great, after a clean install of iOS11 is suddenly slow. None of my Apple devices is working properly anymore (iPhone 5s, iPad Pro 12.9 2nd gen, and iPad Air 2), this is ridiculous, they don't know how to sell more devices that their latest innovation is to make the keyboard and performance so bad and laggy to push consumers to the point that is easier to buy a new devices instead.
And if your answers to all of this is "just get and android", "don't buy Apple", "software is like that, they will fix the bugs", let me tell you respectfully that you are right in giving those advices even if you don't get to tell other people what to do. You are right except in the last part, software is not like that.