In WoW, for example, everything revolves around combat - and any secondary skills (mining, enchanting, etc.) are support for combat, or require combat to advance.
several options, tweak values to taste:
- Give defending players a boost/advantage against attackers until the winnable spoils are too lame to be worth the effort.
- Let there be a magical force which returns 90% (x%) of a loser's stuff to their magic box. Therefore the winnable spoils are too lame to be worth the effort.
- Allow "titling" of real estate and expensive personal possessions. Upon death, the title would be transferred by pre-set rules to someone specific, or in estate court to next-of-kin (respawned player). NPC Shops call the guards if they see mis-titled sales. Guards do random searches at the city gates and confiscate mistitled items. Those are then eventually returned to the next-of-kin/etc.
- Provide an option for mutual "yes lets fight!" where no taxes/boosts/etc are applied and winner takes all/most. (maybe they could agree on custom % of spoils too).
This is it really. I've tried a few such games over the years and it felt like a majority of people were just trying to get powerful enough to kill & loot other players a little under their strength and then repeat the process to bootstrap themselves higher & higher. Players that want to play that way are attracted to such games, and they inevitably drive out players who want the balance shifted a little in the other direction.
I don't see how game design can easily shift this balance because it's more about attracting a different balance of players than in how you design the game itself.