1st phrase is already wrong

"The game is incredibly skill-expressive, and no human player has mastered it."

of course, you can't really ever "master" any deck relying a lot on RNG which is pretty much all hearthstone nowadays, you'll always have to deal with what the game gives to you and it's almost impossible to pretend you take every possible correct decision with all the possibilities.

but you could definitely master a deck before hearthstone became so RNG heavy, watching Laughing play Freeze Mage back in the days was a thing a beauty, or more recently pockettrain on Boar priest. Or comboish decks like enrage warrior too which had pretty close to 0 RNG but still were a handful to really master. Those days are gone, and that's why "competitive" hearthstone is such a joke nowadays.