Having literally just encountered Volition, I'm still thinking about the project as a whole but this is an incredible question for sure, glad to hear people are thinking this deep into it.
Maybe the best idea is to errata, nerf or ban cards as and when necessary? I agree that balance is essential to any card game and errata and nerfs are key to maintain this and I think most players know this too. I feel like players will ask themselves the same question, "Yes, this card is super strong right now but because it's that strong, should I really buy it? It might get banned..." and that isn't necessarily a bad thing in my opinion.
If a player were to buy a card that is incredibly strong, they should be aware that it may get banned or errata'd at any time. The same applies to any other CCG. Every time a set is released in any CCG, the meta shifts. There's a new strongest deck, new strongest cards that blow the game wide open. Those strong cards surge in price and people buy them. But those same people know that there is a risk in buying those cards and when they get banned, they understand and continue playing. I don't see why the same thing couldn't work in Volition.
In regards to created/crafted/edited cards, I still have the same idea in mind. If you create or craft a card that is simply incredible and smashes through everything, then you have to know that there is a risk of it being dealt with to give everyone a fighting chance. Saying that, I feel that crafted cards will need a more precise judgement. If a card is only beating the meta at the time, then I don't see a need for an instant ban or nerf. But if it's crushing every shift in meta and is all-round silly, then yeah! Give people a chance! Players should understand that yknow!
Anyway, that's my opinion. Players know that what they're buying could be removed from the game or nerfed (and in turn, they could be readded or amended), but they still purchase cards or upgrade digital assets in video games, knowing there is a level of risk. Why should Volition have to behave any differently?