I’m pro-PvP but you have to get this, you do PvP in isometric ARPG for “fun”. In no way it’s a reliable way to gauge player skill as there are so many dice rolls included when progressing your character.
You can’t have full control in the situation and your tactical knowledge won’t go further than estimating closed cards (your enemy’s skill cooldowns) and abusing some environmental hazards as shown in official site and videos.
With this in mind, also consider without active trading communities to set up some rulesets it will not be a long lasting affair. Community has to be involved to make PvP somewhat fair for both parties. Otherwise free overworld PvP has its own flaws but it’s all just for fun and you shouldn’t take it serious in any way. Since PvP will be largely tied to trading communities, you can also say that the audience will be pretty small as well.