The problem is there is no SINGULAR definition for "Pay to Win" because it's subjective.

Some games like World of Tanks as mentioned by Myrdin there's a clear advantage to paying, to the point it's very difficult for F2Ps to compete. Most would agree these are P2W.

Most people would also agree purely cosmetic effects like Myrdin's description of LoL (or 99% of SWTOR's Cartel Market, etc.) do not constitute P2W since these have no gameplay effects.

However, in cases like FKG, there are two issues:
1) Convenience - Everything you buy in FKG could be obtained with sufficient gaming time. Does this constitute P2W, since you get it faster? Or does it not, since you can get it without paying, it just takes time?
2) There is no PVP system, therefore, how do you "win"? Is it even POSSIBLE to "P2W" if there is no competition in-game (beyond players being like "well I completed Ultimate Map 79 and you struggle with Moderate 12" which exists in EVERY GAME IN EXISTENCE to some extent)?

Since it is agreed that 5/6*s are not REQUIRED to beat maps in FKG, paying is not strictly required to win (even ignoring the fact you do get occasional gacha chances and event 5*s). Therefore, the two above factors, and how you view them, determine whether this game, and others like it, are "P2W" or not.

Zandel clearly determines P2W to include the convenience factor, and that the lack of PVP is irrelevant. EAB clearly has the opposite stance on both factors. Is one "correct" and the other "incorrect"?

To quote Obi-Wan Kenobi:
"Many of the truths we cling to depend greatly on our point of view"