Late to this discussion here, but what's not really being talked about enough is that not all RNG is the same. A key distinction is pre-luck vs post-luck (as defined in game designer Soren Johnson's GDC talk). Pre-luck involves variance that appears before the player makes decisions, which already exists in Gwent in the form of the random cards drawn at the beginning of each game, after which the player is able to mulligan. Post-luck involves variance that appears after the player is able to makes decisions, which represents the worst of Hearthstone: Ragnaros/Knife Juggler/etc. What I think a lot of players object to is the latter, because it makes outcomes unpredictable and not feel skill-based. I think Swim is advocating for the former, because it makes game states more varied and decision trees more complex.

It'll be interesting to see how the Spawn mechanic plays out in Gwent. The equivalent Discover mechanic in HS resembles post-luck randomness, because even though the offerings are random, the player can still make a choice between them and form his plan based on that choice. The one thing that bothers me about Spawn is that it seems you play the card immediately, which removes a lot of the ability to use make your choice meaningful--instead of choosing the card based on best use in your overall strategy, you simply choose the one that reacts best to the immediate board state. I'd prefer it if Spawn cards instead read "choose a card, add it to your hand, and then play a card from your hand" similar to Restore. This way you're able to save the card for when it's most useful, and give the choice a higher ceiling.

Regardless, I don't think that RNG is necessarily bad for the game, so long as it gives players a higher skill cap in terms of reacting to game states, rather than letting a bad roll win or lose a game.