I think its quite funny, ...
People do something, get punished for "Violating Rule X", and then you argue that Rule X is meant for something Different.
I mean, the ones who would actually know what falls under what rule, would be the ones who enforce said rules. Sure there might be some errors in Judgement here and there, but thats another Topic.
But on your Example, if the rule for Disrupting RP Activities would be that black and white, it would just state: "You are not allowed to sit with your fat ass mount on other People/Activities"
Rules are made broader to include many things. If you would make a rule for every single incident that could occur, your would need quite a large RuleBook.
Point here is:
There are Rules against disruptive Gameplay, be it disrupting RP, or even normal GamePlay, however they are worded, their basic focus is:
Protecting players from Disruptive Gameplay, whatever this is, can and probably will be judged by a Case per Case basis. Even if you say: "This is just PVP, this is Perfectly Fine". There was and will always be a very fine line between: "PVP" and "Griefing".
Anyhow:
With the way this "PVP Guild" was described by other players, I would think they step over that line quite often, and are now Getting the harsher Punishments, after beeing warned quite some other times.
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Okey, ...
No one ever said they were PVP Gods, what I´ve read quite the Opposite.
This is not related to the Story, at all. Hurray, people do different things in the game.
This here is probably the point: Its one thing to raid a City in PVP, stomp everything, kill the King and return.
But occupying the Main Faction Hub and killing everything in sight for 2-3 Hours is (apparently) not Okey.
That remark there discredits your entire Story. You occupied the entire Faction Hub for 2-3 Hours without regards to the other players, and probably ruined some of their evenings. How would you feel if you come home from a Hard day at work, and want to relax for 2-3 Hours before you go to bed, and you log into that shit show?
Probably in the Past, and and maybe said evening the RaidLead/GuildLead got contacted by a GM to ask to stop that. And he Ignored it.
Also doesnt really matter to the Story. I mean I dont play RP, and even I know to stay clear of the Inofficial E-RP server in my Region. Its Weird, but they keep to themselves on their Server, so to each their own fun, dont hurt no one, afaik.
Sounds to me, like you should´ve investigated the Guild just a little bit before joining. I mean if its that Infamous that you get 3day banns after just one Event.