The DC Circuit is majority political hacks. Everything in DC is majority DEM/left/marxist conclusions in strained constitutional rhetoric.
That it is even entertaining this, en banc, is a stain. Regardless of the outcome. The court is knowingly using punishment by process. It knows Sullivan is out of line, it knows Flynn should have been out from under the government frameup since end of May, but now two courts, Sullivan and the DC Circuit think it better to hold up.
No matter how it decides, the loser will be petitioning to SCOTUS. It knew this going in too, and is doing what it can to inflict maximum delay in resolution.
Punishment by process.
What if Sullivan, hoping to force Trump to pardon or commute before the election, proceeds to sentence Flynn?