You might be right. But in the conclusion(s) the OP cited, what are the arguments? Or what are Frame's arguments?
As I mentioned above, Frame's words above seem to have been a simple response to a question by email. He doesn't have the time to fully elaborate the argument behind all of those conclusions. I think he has made the arguments for this particular issue both in DKG and in Apologetics to the Glory of God.
And I don't mean to say that Frame has fully backed up all of his conclusions. Sure, there are some things in DKG and in his newer Doctrine of the Christian Life that could be more expanded. But to generally characterize him as making assertions without backing them up is an unfair characterization of the time he has put into many of these issues.