In International Relations, my #1 or #2 hobby, credibility does not refer to soft power. (my number 1 hobby is philosophy)
Not sure its worth dissecting this, but there is a lot of grey area in your claim of the meaning of Credibility. (Credibility and cultural attraction? Pretty sure these have little correlation. Dictators can make creditable threats.) Further, its a debatable claim that there is a 'core currency' of soft power.
As a contextualist, I am not going to die on this hill for your personal meaning of Credibility. But I can attest that your conviction in your claim is stronger than any International Relations Realist practitioner would make.
It's a shame we can't have nice things.