Again Max, I accept absolutely that the usage of addressing some clergy, especially bishops and monks is ancient, and its application to priests is an extension that is not hard to understand. 

Still, there is a difference, surely, between Paul's (or anyone's) use of fatherhood as a "metaphor" for the relationship of apostles/clergy to converts/faithful and a custom of "addressing" every priest as Father.

As for the scripture, I think you may be taking my observation that such usage is proscribed way too seriously. I am not arguing that the practice ought to be condemned because it is specifically cited by Jesus as a no-no. Still, given that the literal (and allegorical) interpretation of scripture has been normative through most of Christian history, surely the contraction is weird/humorous/surprising/strange, wouldn't you say? If people back then had access to bibles and new its contents as well as people do today, it is hard to imagine this custom emerging.