I've been playing for less than 2 weeks and already multiple times on Olvia channels I've had some Berserker follow me around and hit every single mob I'm hitting, standing quite literally directly on top of my character.

I've been playing MMO's since 2003 and and I have never seen this type of behavior. It's actually insane and I couldn't believe It at first. I then I asked around and apparently it's "normal" here. That's disgusting.

New players will not tolerate it and will swiftly quit. This will reduce your revenue greatly. 

Please consider changing mob claiming rules(anyone within x radius mob dying gets loot and xp), zero cooldown infinite duration marni realms that your party members can join, or hire more GMs to quickly jail and supsend griefers.

I started this game with a group of 30 MMO vet friends who have been playing MMO's since ~1999(everquest / ultima online etc) and I am the only one left playing. They all quit due to griefers. These are adults who make 150k+/year and were willing to drop thousands on this. That's a lot of revenue lost just due to some griefers.

Why not chance channel ? Problem solved......

This is a shallow response. Why should I have to leave because somebody else decides to grind over me? Do I have no agency over my gameplay? Why should I be fully at the mercy of other people? To another point, why can't we grind together? Why is THAT a limitation?
What gameplay benefit does this aspect support? Is it just to let the indignant and entitled players have their way? It is entirely possible that whenever he DOES swap servers, the same will happen. What then? What about spots that marni isn't available? What about when you don't have marni available? What about group spots? Why am I the one punished when I kill someone doing this? They actively have nothing to lose, They are the one griefing very clearly, so why am I the one being punished? The system is deeply flawed, and the changes as of late have only exacerbated the issue.

How do you propose the game differentiate between the Righteous Player that is defending their grind spot and the Griefer that comes in and kills you repeatedly without warning to get you out of the spot?  That is the crux of the matter, isn't it?

OP, I've never had access to the Olvia servers, so I had no idea this was happening over there.  That is very unfortunately.  If it happens to be the same player doing this repeatedly, you might want to report them.

Other than that, if you are on a season character, you can play in season servers for more server options, or on whatever regular servers your guild made their home channels.

As I said it's also something I've never seen in 20 years of playing different MMO's. I don't get why it's so rampant here, but the developers must intentionally do something that encourages and fosters such behavior, since it doesn't happen anywhere else that I've seen.

The developers need to take a long hard look at their game and fix if they want it to grow and generate more revenue, instead of slowly die as vets are replaced by no new players.

This is only one side of the problem IMO, The necessity to fight over a spot in the first place is the real crux of the issue IMO. We should just be able to grind solo spots in parties, with the monsters becoming stronger to suit the party size. I made a post going over my thoughts on the whole situation, and the idea I had was to allow party grinds at solo spots within marni's realm.

To answer your question though, I would think first of all that karma loss should be based on the Family's highest gear set, rather than character, given Karma is a family wide stat now. This would as a result effectively remove karma bombing unless the person truly has that little gear. As for how to differentiate them, I would argue they already are differentaited, as the person defending their spot wouldn't need to flag back in order to attack them, since the attacker flagged first. Killing the attacker doesn't incur karma because they attacked first, so in this case it isn't an issue.

That said, I also think that the punishment of negative karma should be relative to how negative you actually are. I don't think it makes sense for somebody at -1000 karma to have the same detriments as someone at -1000000 karma. The effort given to get to these levels of karma is vastly different.

Idk if this happens a lot on Olvia servers because I don't have access and haven't had acces in years. However, on normal servers this hardly ever happens. I've played this game consistently for years and I run into this kinda thing maybe once every 3 or 4 months. With home servers, the shortened server cooldown, and the recent marni realm changes it's absolutely something you can easily avoid. Now I'm not saying any of that is a true solution, and I do think more agressive moderation is needed.