Using SQL workarounds/hacks just makes the code harder to read and harder for the query optimizer to detect the original intention and optimize in the future.
This is true, but the workaround proposed in the article is not a change to the query at all. It's adding another index, which is a pretty classic case of "proper" usage of query analysis (as opposed to confusing/hacky mutations of the query itself).
Unless I'm misreading they didn't add another index. They actually just reduced the original index by removing an indexed expression and excluding rows that didn't match that expression instead.