How so? Does the class start at max level? If that's listed on the link you showed me then please quote it. What in that article "proves" that class is more powerful or "better" than the other classes? Please provide exact quotations from the article. Otherwise it just sounds like you're assuming. Let me give you an example of how to prove something using a similar situation.
In DCUO you can "buy classes" but they are not any better than the other classes in the game. They've added Green Lantern, Earth, and Electricity "classes" to the game in purchasable DLC packs. These 3 classes are not any stronger than the 6 starting classes (Mind, Sorcery, Fire, Ice, Tech, and Nature). DCUO breaks up their classes into 3 roles, Tank, Healer, and Control (any class can also DPS). Green Lantern added another option for players who like the control role. Earth added another option for players who like the tank role. Electricity added another option for players who like the healing role. These 3 new classes are not any stronger than the original tanks, healers, and controllers. It just added new playstyles to these same roles.
Now please provide evidence how the class you have to buy in LOTRO is stronger than the base classes. Do is start at a higher level? Does it get stronger abilities? Does it fulfill a role no other class can? Are they required to form groups? These are just some of the elements that would make this class imbalanced. The article you linked didn't mention any of these things. So if I missed them please provide some quotes. Otherwise to me it seems no different than "buying classes" in DCUO which did not make you any stronger, but just gave you more options. Again; please provide evidence this class is stronger than the other classes, and how a player who buys this class will be objectively better than all of the players who didn't buy this class.
Edit: Seeing your post up to. Are the unlockable heroes in LoL (I don't play) outright better than the heroes you start with? If not then it's not a pay-to-win model. It's only pay-to-win if the purchase makes you stronger. What evidence have you provided that the purchasable classes are just outright better?