I don't play Fortnite but I see "V-Bucks" available to purchase from the Microsoft store, so I assume it's the same.
Anyone with enough money can just go buy all the upgrades and dominate.
Maybe those cheating don't have the money to buy the gear, so they're trying to level the field in a way that's reachable to them.
edit: apparently the pay-to-play upgrades in Fortnite are cosmetic only. Not sure about the others.
I've only played save the world. Which is a small team against a computer. That is where you get these card packs. Which you give heros, survivors, traps, materials, weapons, etc.
Was going off the description "...In Save the World you can purchase Llama Pinata card packs that contain weapon, trap and gadget schematics..."
in which I took weapon, trap, and gadget schematics to mean something that could give you an advantage.
Monetary exchange through this game, and many others, in this format of money for cosmetic content does not alter the gameplay mechanics in any way.
At best you could argue a marginal camouflage impact, but that is so minor it is effectively non-existent.
Many many games have taken this model, though. I love TCG games, but they're so stupidly expensive and pay to win I've given up.