It seems many define "winning" strictly from the point of view of PVP. This may be familiar to people who have played arena PVP type games, mostly F2P titles, that sell "god mode" items directly in the cash shop, items that let you essentially auto-win against another human opponent who hasn't paid for a similar buff.
However I think this definition is far too narrow. I think to define "pay to win" you must first define "what is WINNING?", and I feel that will vary depending on the nature of the game you are playing.
In the context of a purely PVP arena game yes, defeating your enemy (another player) in combat is the only real victory to be achieved. But the range of goals, activities, and rewards in an MMORPG are much more complex, and the things one can "win at" much more broadly defined because of it. Therefor I think it is dishonest to use the same definition of "what is winning" to apply to MMORPGs as one would to describe "winning" in a PVP arena game.
There is a whole complex school of psychology surrounding MMORPG's and what motivates people to play them. Some say it is a need for validation. Some say it is addiction. Some see it as a way to escape their lives while others see it simply as entertainment or "brain exercise," an outlet for creative imagination, or just a forum for interaction with other people.
I have noticed people (game developers specifically) tend to be very sensitive regarding their own pet theories about what drives MMORPG sales, yet for all their insistence on one gimmick or fad or assumption about human nature based on rat studies or whatever, essentially NO MMORPG has managed to get "the formula" exactly right over any protracted period. Not since WoW during the height of Burning Crusade and Wrath of the Lich King and the BILLIONS of dollars (yes, with a 'b') that Blizzard made during that period have the stars of this elusive and esoteric equation aligned so perfectly.
I think this is in part because MMO companies today tend to be far more concerned with chasing fads and gimmicks and cash shop profits in the short term than making games with HEART and PASSION that last, but that is another conversation.
The point is, I believe that "winning" in an MMORPG has to take into account some of this same psychology about what motivates people to play them. THAT, I believe, is what would constitute "winning" FOR THEM.
While it is an admittedly complex field of sociology, one driving theme that has been well established is the "sense of accomplishment," which is why people seek completion ("gotta catch 'em all"), and work towards achievements, titles, rep grinds, or other unique means of establishing themselves apart from other players. It is what sells mounts and vanity items and keeps people hunting for motifs, leveling up crafting professions, etc.
Now, consider the recent addition of crafting research shortcuts to the Crown store. In this game, taking the time to do the research to be able to craft more niche gear sets like Pelinal or Twice Born Star used to be one of those things that set people who did it apart and thus, SOMETHING OF VALUE to them. Guilds had "guild crafters" that would make these sets, and it made people feel sort of important because they had something to offer more than just showing up with a credit card. It showed they played the game, they had been around, they were veterans.
This sense of personal accomplishment and setting one's role apart is precisely what is undermined by simply selling these things to whoever throws money at the Crown Store, and since that sense of uniqueness and importance to the group is what was "winning" to the completionist MMORPG player, and since the person buying it ostensibly seeks these abilities for the same reason, TO FEEL IMPORTANT, or to undermine the importance of others, I would say that is pretty directly pay to win in this context.
Consider, why someone would care if they won or not against their opponent in a PVP arena game? Why does it really matter if someone pays for an OP buff that makes their virtual pixels defeat your virtual pixels in imaginary combat? BECAUSE IT MAKES YOU FEEL GOOD TO WIN. It is the same for people's sense of accomplishment in crafting, in titles, whatever.
Different definitions, different opinions, different gaming genres, but you cannot deny that someone just showing up with money and buying the whole guild something is going to upset the person that invested time and care into building up the ability to provide that service when their role is rendered superfluous overnight by someone's credit card.
I think a very important point to consider in these discussions is that just because it doesn't matter to you doesn't make it right to marginalize what is important to others when making assumptions about what is "valuable" and what is "winning."