Buying lesser charms is buying a currency that can only be used to participate in a loot lottery. That is exactly what it is. No more, no less. That's not what the sub pays for because you don't need to participate in any random looting to play the game; but there is no further outlay if you do want to participate in those lotteries.
OpenRaid is a total strawman. You don't pay them, and you don't use it to participate in a loot lottery. If you use it with that intention in mind, that's up to you and if you use it to pay other players to help you toward that goal, you're breaking the ToS.Tell me what do you have a chance to get from lesser charms? You always win with lesser charms because you have a 100% chance per week of winning three greater charms. You aren't paying for the chance at loot. You always gamble on the chance an item drops no matter what you do in WoW. That is how random loot works. But you aren't breaking the terms of service by gambling in that way.
You aren't paying money for a chance at something. You are paying money for lesser charms. Your chance at something has no baring on how many lesser charms you buy. Because lesser charms don't give you a bonus roll. Again your employer isn't gambling if you use your pay check at a casino. Just as Blizzard isn't running a casino if you buy lesser charms then use those lesser charms on something.
Gambling requires direct cause and effect. If Blizzard is a casino and will run into problems with EU/NA gambling laws then Openraid is a casino as well (just one that doesn't charge for entry) because both enable gambling. For that matter the very act of random loot by your own logic would be gambling and against the law. But we know none of these are true.