The Acting Director being fireable at will may not be enough to overcome the pernicious problem of the POTUS having enough control over one of his federal agencies.
Under HERA, if the POTUS fires the Acting Director he cannot choose a replacement that is aligned with his beliefs and desires for the future of the Agency, he must pick from 1 of 3 deputy directors chosen by the current FHFA Director. There are also imposed on him under the Federal Vacancies Reform Act further restrictions on just how long his Acting Director can serve before getting a Senate confirmed Director in there. In this particular fact pattern, OBama said he was unable to remove Lockhart.
But if the SCOTUS wants to do a remedial dodge on the Severability Analysis relief section of the Collins case, I think they could maybe find a way. As this case was making its way up to the SCOTUS, many Judges expressed skepticism about giving retrospective relief. I thought David Thompson had a good answer to Justice Sotomayors question, "Why should YOU be entitled to anything?". Answer: Because Seila Law last term said that the Plaintiffs are entitled to retrospective relief and it was granted in some other cases in the past. Also, footnote 11 in the Free Enterprise case said that the Plaintiffs need not create a but for world.
Of course, I am pretty sure that Justice Thomas and Gorsuch are itching to OVERRULE HUMPHREYS EXECUTOR, if you read their reasoning in Seila Law, but can they get ACB, Kavanaugh, Alito, or Roberts to join them? Good times, Good times!