On the other hand 'banned for [duration]' and 'temporary ban' have definitely been in use for a long time, which I personally have never thought seems wrong. I

On the other hand 'banned for [duration]' and 'temporary ban' have definitely been in use for a long time, which I personally have never thought seems wrong. If those uses are in play, 'permanently banned' can actually be motivated for disambiguation. And I would suggest '[permanent] suspension' may have connotations of a statement about reversibility. 'We have the ability to reverse this action [but we intend not to exercise that ability, ever].'