The Separation of Powers isn't necessary in congressionally chartered private corporations like FnF, because the Agency's Powers are limited to comply with the Charter.
This is what the Scotus-appointed amicus, professor Nielson, explained in his written statement.
Thus, the Supreme Court should only have struck down the duty (v) of the director when FHFA is Regulator: "activities in the public interest" and maintain the removal-for-cause provision and "independent Agency of the Govt."
Read my previous comment about Justice Alito, the conman.