When I initially wrote the article I said this was very unfortunate, because this seemed like planned obsolescence, older phones being made slower.
In this case, though, it's not based on the age of the phone; it's based on the ability of the battery to provide the power that the phone needs. Apple was dealing with a particular issue where their phones were shutting down abruptly. Given the option between a phone that shuts down abruptly and a phone that operates slightly slower, they made the decision that a slower phone was better.
Regarding Apple's perhaps lack of transparency around that issue, I'm not sure what they should have done. The lack of transparency was certainly disappointing and could definitely lead people to say this was an issue of planned obsolescence. However, I certainly don't think that's the case.