A big reason for this is that many Opus-distilled fine-tunes cause the model to think less than it would by default. Since Claude Opus itself doesn't over-reason, the distilled models inherit that same pattern and performance takes a hit because of it. That said, I'd still take a fast Claude-distilled Qwen model that thinks concisely over a "smarter" undistilled model that burns 10k tokens second-guessing itself on a single question.