If it were me, I'd say that while this is borderline on the exploitation it's also unprecedented. Hand them a warning - or temp ban - but anyone else doing this in future is banned.
I don't know everything about this case, but on the surface it sounds like a pretty ingenious plan and one is have been fairly happy with if I'd thought of it. No game exploits were used. No different from any other in game deception. An outright ban seems harsh.
What I'd like to know is: how did the slaver(s) respond when "slaves" complained to them in game via comms? (If the slaves did indeed complain?) Were the slavers insulting or abusive? That might be one reason for a ban.
Why though? It's legit gameplay and teaches valuable lessons without harm done.
It required new players to listen to their "slavers" and fit their ship without a fuel scoop (lesson one: never skip on fuel scoops if landing on a carrier)
and most even told to fit 2D frame shifts (lesson two: you never go 2D frame shift, not even in PvP any more).
And the general lesson is, people can be jerks, don't trust randoms on internet. In german we have a saying for this "Gier frisst Hirn" (greed eats your brain).
Nothing except time is lost for the "slaves" here. It was all legit gameplay. No botting, no real money extortion*. Just people playing dumb other people.
And children should learn this lesson, too. The harm done here is comparatively small.
* in case those "slavers" asked for Arx or real word money etc. a ban would definitely be on the table though.
edit
Nah, not buying it. Try playing something like ARK and see how that goes. Hell, it's a legitimate mechanic in there, and you only have to read the T&Cs to know FDev mean "in the real world", not in game.
Besides, I've never seen anyone excluded from a game mode before. Just "Open"? Hmm!
Shadow bans have always been a thing in Elite. Restriction to solo play before the account gets canned completely. Or so I heard.