According to Gamasutra, World of Tanks used to give an edge to paying players, but fortunately the developer Wargaming.net promised to "remove all "pay-to-win" purchase options from all of its current and upcoming titles."
Do all players now have an equal chance to win, or do paying customers still have an advantage over free players? For example, do paying customers have more garage space or unlock new items and vehicles at faster rate?
A definition for a pay-to-win game:
A common suggestion for avoiding pay-to-win is that payments should only be used to broaden the experience without affecting gameplay. For example, Dota 2 only allows the purchase of cosmetic items, meaning that a "free-to-play player" will be on the same level as a player who has spent money on the game.
Best Answer
The features like extra garage space, higher earnings and easier access to higher tiers are not the "P2W" problem - that's all a metagame, paying players have it easier there, but it doesn't give them competitive edge because they are still matched with players of the same level (paying or not). The actual game is played during battles, and these elements don't provide advantages over players you're pitted against. It doesn't matter how many different tanks you have, what matters is what percentage of battles you win and how many enemies you damage.
This is unfortunately, where WoT doesn't shine. Yes, you can excuse the "gold ammo" - special ammunition that while possible to purchase for the "free" currency, makes gameplay completely unsustainable (even massive victories will create a big budget defficit). So, if you want to "spam gold" (shoot copious amounts of the premium ammo) you'll need to pay - and you'll get a significant edge over players who just can't afford it.
But that's not the end of it. What matters a lot is performance of tanks. The game inherently has some imbalance making some tanks better and some worse; but never before had the imbalance been shifted so much towards Premium tanks - obtainable for gold.
The paradigm used to be "Premium tanks are meant to be middle ground, somewhat inferior to maximally upgraded standard tanks." This is no longer the case. The most blatant example is Object 252U Defender, a relatively recent addition; a premium tank that is supposed to be quite similar to IS-3.
Well, it isn't. The "free" IS-3, while similar, has inferior gun penetration, vulnerable frontal plate, and some more protruding cupola (weak spot on top). Generally, Defender is objectively far superior. But Defender can be purchased for 10,950 gold, that's around $42. IS-3 requires a lengthy grind.
And as for earning gold in-game - that's a fallacious argument that crashes in contact with reality. You can obtain a little gold here and there in various rewards for events etc, but you'd need literal decades to accumulate 10,000 of it that way. Any considerable amounts of gold to be earned can be only earned through winning high-level battles with advanced, high-level clans; in particular not any clans, only GOOD ones. And to join such a clan, you need exceptional skill, time, dedication - and GOOD tanks. Like Defender. It's a Catch-22: to start earning gold, you need to first have, and spend a lot of gold - to obtain superior - "pay to win" - tanks. Never mind some of the best premium tanks can't even be bought with in-game gold (earnable in game); you can only purchase them at the premium shop for real money.