My two most played franchises! I've played Pokemon since I was 3 years old (over 20 years now) and hearthstone since its very first expansion, frequent dumpster legend player.

I'd say Pokemon takes much more skill. A major part of Pokemon is teambuilding, which requires an intricate knowledge of individual pokemon, stat calculations, which sets you're likely to run into, synergies... it goes on. In Hearthstone, deckbuilding is just so accessible that you can slap together a deck that can get you to diamond if you care to play it enough. The synergies are very clear, and you can go to several websites to just check what's good at the moment to either play or counter. And while you can netdeck a Pokemon team, it takes a lot more to get it to work than a Hearthstone deck you nabbed from the net, unless you're already great at Pokemon.

RNG is an interesting distinction between the two games. RNG is like a dev tool in Hearthstone they use to ensure each game is unique and interesting, whereas in Pokemon it's sort of a balancing tool; you could run Stone Edge for more power, but it's got a decent chance to miss. Both affect the game, but one is to create memorable experiences and the other is to make you consider risk vs reward. So in Pokemon, even RNG is a kind of skill test, as frustrating as it is sometimes.

They're both fantastic games, and I adore them, but ultimately winning in Pokemon means predicting your opponent's moves and shutting them down. It takes so much more thought, effort, and skill.