p2w = you got for your money something that is not reachable without them.
FoE until now have everything doable without money. OK, it takes 2x, 3x more times but it was possible.
It does not matter, if you got some OP bonus or just 1 special portrait. If you must pay to get it, it is pay to win.
well it's not like the definition is set in stone really. I look at gaming like this;
A) a directly purchased game where nothing can be bought or changed
B) a directly purchased/subscription game where nothing can be bought that changes your game aesthetically but not competitively
C) a free game where nothing can be bought or changed
D) a free game where stuff can be bought that changes your game aesthetically and competitively
So I put FoE in category D. Of course, you could always do everything on FoE but relative to the guy buying 40 Cherry Blossom Set's you're playing the f2p version and he's playing the p2w version.
To bring it back around on topic, while I agree these Leagues will favor the diamond spenders it's only part of the event which non diamond spenders can still take part of and gain the same things, the diamonds spenders just get a bit more is all and that's not unusual for a diamond spender to get more. Also it's never guaranteed everyone will get the main event stuff in every event. And with sets and upgrade pieces not everyone is guaranteed a full set or a fully upgraded building, that's also the incentive structure built in to spend diamonds.