I'd say that if I had solid, unshifting requirements and not much else, I'd do better than I would without them, but with everything else. Would you disagree?

No, I wouldn't disagree.

If I had a little man that could spin straw into gold I'd have much less trouble paying the rent each month. Would you disagree? :-)

In my opinion fixed requirements are one of those harmful lies we tell ourselves. It encourages us to focus on the impossible (fixing the requirements in stone), blame the wrong people (it would of worked if the client hadn't changed things) and prevents us addressing the real problem (finding a process that can deal with the reality of changing requirements).