What's weird is I didn't see mention of accuracy in the article.

Not really. Haiku is really not good at decision tasks (source: real experience).

Right. So we can either assume the engineers at Amazon are fucking clowns who don't do any engineering, or we can assume they tested and found that Sonnet was the cheapest model that met their reliability targets.

If you think the former is a likely hypothesis, then why did you even click on TFA?