I mean you don't have to buy anything in Hearthstone unless you are impatient and want everything now now now. I'll have to check out Infinity Wars though. I am not all that good at card games, but I love them lol.
I also played Hearthstone and my main gripe with it is that its simply too simple. Its like a card game for people who like things easy. Which seeing as how its made by blizzard i totally understand. But the one thing i like about card games is there being tons of strategy and complexity.
Thats pretty much what was going on through my head as i was playing.
That said if you like the game and have fun playing. Who cares about anything else. But yeah when u have some extra time i do think you should check out Infinity Wars.