I don't worry about the warrants. There is no way they can exercise the warrants, given the loans have been fully repaid.
79.9% free warrants is a just-in-case arrangement that the GSEs shall bankrupt. The arrangement will guarantee USG can recoup as much as possible from the GSEs.
And, I think you should include the NWS overpayment into your calculation. It is over $10B, after all the principle and interest payments.