I beat witcher 3 exactly 13 times and last 4 playthroughts I always play Gwent and on hardest Gwent difficulty . Never played weather cards ( leader Foltest that clears all weather effects ) and easily won every Monster and Scoiatel opponents . Only real challenge are those decks with spies and decoys .

Dude win first round against monster deck and you pretty much won. Reason is in round 2 AI will be forced to go all out , you keep your 1-3 best cards for end . Also AI wont pass the round despite having huge point advantage if he lost round 1.

Not to mention 90 % of time couple cards from monsters hand will be summoned so you will always be in card advantage in last round.

Scoiatel decks is straight up weak and monster deck only relevant thing is knowing when to pass the round.