Yeah, no, I agree. But my experience with it has also been that as soon as you start writing anything except simple code, its performance starts to suffer, while Chez handles complex abstractions more gracefully. So I suppose comparing them directly might be a bit unfair both ways.
Can't claim I remember much detail given how long I haven't worked with it. IIRC one of the issues had to do with tossing around anonymous functions inevitably causing it to give up on JITing and drop out into the interpreter