What I'm suggesting is to empower the player with UX controls at their immediate disposal. Most of the time third party player characters are really great. The issue is that when they aren't, there is no ability within the primary player's control to immediately resolve the situation. This is an extremely simple solution that leverages already existing features.

If this wasn't an known issue, then why are GMs issuing 9 day bans for the griefing and obstructive play?

Just give the player the ability to turn off non-party player characters in their own System Configuration. Problem solved.