The author does a good job explaining how join diagrams are more accurate than venn diagrams, but by saying that venn diagrams are bad and wrong, I feel like they completely miss the point. The venn diagrams can be understood almost instantly, whereas the join diagrams take time and thought to take in.

If someone was brand new to sql joins, sure maybe I would say a join diagram is better for them, so they can really understand what is happening. But for someone who just wants a refresher on join types they rarely use, I think the venn diagrams win. I guess ultimately I don't like the claim that one type of diagram is simply "better".