I also have the same question. That said, for some problems, at least over the last week or so, I did sometimes get better results from lower-effort Opus or even Sonnet. Sometimes I get (admittedly this is by feels) a better experience from voice mode which uses Haiku. This is somewhat surprising in some ways but maybe not in others. Some possible explanations include: (a) bugs relating to Anthropic's recent post-mortem [1] or (b) a tendency for a more loquacious Claude to get off in the weeds rather than offering a concise answer which invite short back-and-forth conversations and iteration.

[1]: https://www.anthropic.com/engineering/april-23-postmortem ... but also see the September 2025 one at https://www.anthropic.com/engineering/a-postmortem-of-three-...