With the use of Wildcards both from boosters and from the Vault, my experience is that just playing a few matches every now and then is enough for me to quickly acquire the cards I need. I'm sure if you want to be competitive, spending a bit of money for more boosters and a chance at more Wildcards shouldn't be a problem.

However, you can contrast this with Elder Scrolls Legends where, for a few months, I was in the top ~1k players without having spent any money at all. You got plenty of cards as rewards for playing well. You also got a full set of one special card per month as reward for being Legend rank (you didn't even need to reach all the way to Legend).