Ok fine, maybe they had rates before but that doesn't change the fact that this can be seen as a predatory practice if it was on purpose. Once again, the issue is that they did not mention it anywhere in game. If you can complete a purchase without going through the site then they should mention somewhere in game that chances aren't the same for every style. Also Neospector points out that this doesn't apply to every coupon.
You say it's my fault because I made the assumption things worked the same way as before, what about new players? Ones with no history with Nexon? Would it be fair to fault them for the assumption that all the styles are actually random? These coupons even state themselves that the outcome is "random". Randomness is more than uncertain outcomes, it is the lack of any intelligible probability. Out of the 9 styles in the coupon 4 of them are locked behind a 20% chance of appearance, true randomness would be 11.1% for every style. If you have a biased probability of the outcome, it's no longer a "random guess" it's an "educated guess" so to say that these are random and have no additional mention of a biased probability is misleading to say the very least.