The definition of what is considered "Pay to Win" has changed over recent years.
Originally pay to win was defined as paying for items that were superior to anything else that was obtainable through normal game play. for example if the best axe or armor in a game was only available on the cash shop.
Over time though the definition of pay to win has become any micro transaction that gives a player any advantage no matter how small over other players who don't pay. even if those items are considered optional.
This is beause It used to be argued that if said item could also be obtained through normal game play then it wasn't considered pay to win as you could get that item without paying.
However a lot of companies abused this and put those items behind insane grind walls that were almost impossible to pass simply so they could say you don't "have to" pay for the item.
For example the fastest car in a racing game might be obtained for a $15.99 microtransaction or alternatively locked behind an insane grind wall like 50,000 race wins needed to obtain it.
So while that car is technically available without paying it's realistically almost impossilbe for any players who don't pay to obtain. Thus it is still be considered pay to win. Even though that car could technically be acquired without paying. It was deliberately made to be an unrealistic obstacle.
Even things like exp boosters in games can be considered pay to win especially if those game have rank based rewards and skills. As that exp boost would ultimately give players an advantage and allow them to unlock those skils/weaponsl faster than players who don't pay for the boosters.
As such any micro transaction that gives that player an adavantage over other players is generally considered as pay to win.
this is why micro transactions should pretty much be cosmetic only as vanity is pretty much the only thing that offers no advantage to a player.
even additional retainers for example offer players advantages over players who only have 2. and thus could be considered a pay to win element within xiv.