There are 2 reasons. First off.
Recovery Auto Potions. These "luxury items" have been the most ridiculous "pay to win" items I have ever seen in a long time. Is your team not strong enough for that TMQ/UD? Get a "luxury" recovery potion and you'll all easily survive what killed you before! Pitting off 2 Shadow Knights against each other with the exact same +15 gear? The Shadow Knight with the "luxury" autopot will win in EVERY SINGLE CASE. Heck, I've seen plenty of players solo TMQs and UDs they would've never been able to solo without these cash-exclusive steroids.
On top of this they are also terribly imbalanced as they recover ALL your LP instead of a set portion. This makes LP tanks invincible whilst making a far smaller impact on anyone that isn't LP-based. Of every item in the game, these autopots shouldn't just be removed from the cash shop, but be removed from the game entirely and burn in a blazing fire. Yes, I hate them that much.
Second.
Dogi Balls. These Cash Shop exclusive items can be put onto your dogi/hair/mask/halo/etc to give you a boost in stats. Other than pretty much forcing you to wear dogi parts, someone who doesn't cash is missing out on a potential 40+ CON. And when 2 similar Swordsmen face off and one has 40+ CON over the other, we can guess who's gonna win. Making Dogi Ball boosts smaller would just be reducing symptons, not actually taking care of the problem. It's best that these be made in-game obtainable, or better yet, get removed since nobody wants to be forced to wear a silly hat, mask, halo, etc. just to be efficient.
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Buying Equipment Boxes and even Upgrade Stones are really overpowered ways to get ultimate endgame gear, but with much time and grinding someone can achieve the same results. But so long as people can buy Dogi Balls and Recovery Auto Potions, no amount of hard work can overcome the power of cashers, and they will always win through paying. It's true "Pay 2 Win".
I don't know what the plans for DBOG's Open Beta Cash Shop are, but so long as Recovery Auto Potions and Dogi Balls exist, it'll objectively remain P2W. And if Founder's Titles end up getting exclusive stat boosts rather than the same stat boosts of already existing titles, then that will have added another small P2W layer onto the game.