There are numerous alternatives. If you want to reward people for playing, and not forfeiting, grant them xp for playing a certain number of cards. Right now you are rewarding people for forfeiting, then ban them afterwards. How are people to know this is an exploit? If you tell them they are in disbelief, as no reputable company allows an 'exploit' to persist for that long, while continuing to ban people for taking advantage thereof.
Any system would be better than what we have currently.
Honestly, I think the biggest issue in Gwent is communication between the devs and the players. The mods say we cannot attack CDPR for enforcement and I agree that really isn’t productive. If they give you the rules to their game, then that is that. But, I wish they would explain their reasoning, have a dialogue with the player base either via live stream questions or selecting the best written questions and work with the players to figure this out.
Honestly, I think it is more about play rate than forfeiting. If you play 75% of your games, then leaving before playing a card in 25% seems unlikely to get you banned. But if you invert that and play only 25% now your not really contributing to Gwent. Personally, there are certain leaders I refuse to play on casual. It used to be NG, but since MM it is SK or Ethereal monsters. It’s not because I cannot win, it’s because the game is stale against the same decks. I haven’t been banned and honestly don’t expect to be. If I am, then I move on and find something to play. At the end of the day, if you cannot have fun playing Gwent then don’t. If you don’t like a matchup for whatever reason and your not playing ranked, skip it. Just be selective in what you skip and how often and you should be fine.