This is a promising direction! Unfortunately, I think the benchmark result here is essentially meaningless.
I recently discovered this same lesson the hard way. I was trying to get a multi-agent system I was building to improve upon GPQA Diamond scores (system here: http://pellmell.ai). No matter how hard I tried, I could not get any lift. When Fable 5 dropped, it also did not improve upon Opus, and I realized my mistake. The benchmark was saturated!
Now, looking at the result here, I see a similar pattern. Fable is not better than Opus, and the score is ~95%. Notably, this post omits which subagent is being used. Why? An intellectually honest way to tell if this thing really works would be to run that agent and report its score and cost as well.
Going back to my GPQA Diamond lesson, you can see here how a saturated leaderboard behaves https://artificialanalysis.ai/evaluations/gpqa-diamond. Fable gets 92.6% for $0.22 per task while several models score higher for $0.01. I could easily publish a router that “enhances Fable on GPQA Diamond” showing improved score for lower cost, just by implementing a router that picks the model at random!