There is absolutely no doubt that World of Tanks is a pay to win game in the sense that you can clearly buy things helpful for advancement, and not just cosmetic items. But if you consider the idea of paying to win, you need to think about what winning actually means. And it turns out that there are ways in which you can sell "wins" to your customers without upsetting anybody else, because one player's win isn't necessarily another player's loss.

The trick comes from the dual structure that so many games have today: In World of Tanks that is the tank battles on one side, and the garage with its tech trees and tank tiers on the other side. In the tank battles you are in direct competition against other players in a zero-sum game, so selling wins there is a very bad idea, because it upsets the losers. But the garage has no such limitations. Getting to a higher tier faster is desirable for the player, but doesn't give him an advantage in battle, because he will always fight equally strong opponents.

In general, World of Tanks does this very well: The premium account for example gives you no advantage in battle at all, but enables you to advance faster along the tech trees in your garage. The same is true for the various "personal reserves" you can buy, which also boost only garage progress. Even most of the premium tanks are not more powerful than regular tanks in battle, and are more useful for farming credits or crew xp than for winning. A few of the premium tanks are overpowered, but that appears to have been more accidents of design, and often Wargaming realized their mistake and stopped selling the premium tanks that turned out to be too good.

The only point where the pay to win in World of Tanks is really hurtful is the use of premium ammo. It doesn't matter that you can now buy premium ammo for credits; the economy is thus that without a premium account and some gold, the constant use of premium ammo isn't possible. And premium ammo affects the tank battles themselves much more than it affects your advancement along the tech trees. There simply are a lot of situations where without premium ammo you can't hurt an enemy, while with premium ammo you can. You can easily imagine duels of tanks where the use or not of premium ammo would decide the winner. This is pay to win at its worst.

Now Wargaming is planning to review how premium ammo works. Right now premium ammo often is strictly better than regular one, having better penetration for the same base damage. We don't know what will come out of the changes, but one idea is to make premium ammo more situational, giving it less damage for better penetration. It would still be bad "pay to win", but at least it would stop people from just using premium ammo all the time.