Here's the thing:
1. when you play ranked games, you're in most cases matched with players from the same rank
2. people playing this game for years and having large card collection, can easily drop to the ranks you're currently at, so it may seem strange to you, that you're matched up with such "veterans"
3. sure there are people, that used shortcut and bought themselves some cards to play the decks they want, and there's nothing wrong with that
4. maybe it's just me, but I don't consider a game as pay-to-win, when it's totally possible to not spend a penny and still reach the same level as people, who put a lot of money in. It just takes more time. I look at it this way:
- people who bought cards for money, they spent their time at work in order to get the cards they want,
- people who prefer not to buy cards, they need to invest their time to play the game and "farm" in-game resources (a.k.a. in-game currency) in order to get what they want.
In both cases there's some effort to be made. You can argue whether one way is shorther than another, but in general, the game does not close you the way to eventually get the same cards if you decide not to put any money in, and for this reason I don't consider it P2W. The only thing, that you won't get without paying real money, is some cosmetics, but pay-to-look is not what you had in mind after all.