Sol easily outperforms Fable on every task I've tried it on.
Both failed spectacularly. But sol's output at least contained interesting findings and some useful parts, as well as not being 20000 words of unbearable language.
This is where intelligence is not one of a kind, these systems have different pros and cons.
I use Sol as an architect and fable as a brilliant single task solver.
I can tell Sol, "Hey we need to update this core database schema to handle this new use case" and it will masterfully handle the update, version the API, roll the consumers over, including versioning the Kafka schemas, deploying things in sequence, watching the deployments to make sure the new services act actually active before cutting over consumers, exercising the website and mobile apps in staging environments before releasing to production, etc.
Fable just falls over on long horizon tasks, it does partial implementations, it cuts corners, it gives up, it doesn't verify it's work, it loses track of what it's doing, etc.
It's fine for specific well scoped tasks but can't take high level guidance for complex updates.
You could say Sol is faster and cheaper and that's true. Outperforms Fable? Impossible to believe without hard evidence.
Because Claude doesn't allow third party harnesses on their subscriptions I doubt the majority of signals you're getting are actually that significant on pure model quality.
I suspect you're right on Sol not outperforming Fable; but i've not used Fable that much.
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But, fwiw, in my custom harness between Sol & Opus 4.8 - then Sol wins by a ridiculous margin as Opus keeps claiming slightly wrong things with certainty much more.
But I actually prefer it this way. Sol is a master of overengineering and being overly scrupulous, so Fable balances this out, and I can always say "don't listen to Sol's advisory" about 50% of the time.