I think it's good to note in the article that the second query is slow because the RDBMS doesn't use indexes (and which ones). Currently, the text is hand waving the problem and moves on.

If the article had, instead, listed indexes, shown they were used in simple cases, shown they weren't used in the second query, dug into why they weren't (maybe they were but it was still hella slow) - that would be a ton of value!