That gave you an advantage, not an "I-win" button. You still had to be good enough to clear the raid. Give 20 LFR raiders £5000 in WoW tokens to mop up all the BiS pieces they could from the AH & they'd still struggle on Wrathion.
So the game isn't pay to win, unless you think buying a boost so it looks like you've cleared 12/12M or hit Gladiator to be winning. Can you pay for an advantage though? 100%, that's definitely a thing.