You pretty much contradicted yourself. Being a lower level then a person that just bought a 50 is then a disadvantage. While the advantage that level brings is minor it is still an advantage. Buying power, or paying to win, doesn't matter the relevance of that advantage. Only that you can buy one. If we use the argument of relevance then buying full Mythic gear right now would not be pay to win. Because it is the end of the tier and that Mythic gear is going to have no relevance in a few weeks. Because the relevant item levels change.