Does it suck that you can pay to get stronger and make the game unfair? Yep, but I'm not convinced it matters if you're playing casually. None of the pay to win stuff changes the game play drastically. You're only really increasing the amount of damage you do, it's not like Path of Exile where some of the really rare items can enable a new type of build or trading card games where certain cards let you build different decks with different playstyles.
Personally, I see no incentive to buy anything. I can clear a level 12 challenge rift, grind slowly and slowly clear higher level ones. Or I could spend a bunch of money and get to do level 20 challenge rifts or whatever. At which point you hit the wall and either pay money or keep grinding. But since the game is all about grinding, why pay to skip forward and grind more?
Edit: Or right now since it's early you can out-skill other people while they're figuring it out and soon the people who spend more will have both skill and raw power and will dominate