It would be cool to have such a mode as some kind of brawl, where, for example, one player has 40 health, and the other has Nicola from the campaign on the board. Perhaps such a fan-made mod is one of the things that Heroes of Might and Magic is missing.
It's not that it's bad in itself, but how bad does everything have to be overall for playing with pre-built decks in competitive mode to be an option?
Look, a couple of years ago, Hearthstone tried to create a "heroic brawl" once a season. Essentially, it's the same as Grand Prix, but with the pretense of being highly competitive: you invest 1000 gold for one attempt, and if you play well, you win back that amount many times over; if you lose, you end up with a huge loss. The mode didn't appeal to players, and it was replaced by "Brawls" – the same thing, but you invest 150 gold, and the rewards are like those for an Arena run. And recently, they started making fun modes in a similar format – for example, all creatures become 1/1 for 1 mana. Hmm, Grand Prix, we recognize you.
Now, let's look at Gwent. It seems that there are no brawls or Grand Prix there. But there are "seasonal matches" – also a mode for having fun with cards, where there is no balance – everyone plays as Skellige, and other factions are much weaker here. And the main goal – pay attention – is to farm an avatar and a card back. Doesn't that remind you of anything? (However, in Gwent, the card back feels much more valuable – it's currently the only custom card back in the game.)
Now, if you perceive Grand Prix not as a competition, but as a "fun mode for playing cards," then it doesn't seem like such a problem that they appear so often. Let them have it every week, but then make it easier to get cosmetics, and leave shards and legendaries as a reward for the hardcore players. And I won't be surprised if we ever play Grand Prix with Nicola and Ma'ish with 40 health.
To sell my soul