I consider pay to win not too be a quantity matter, ie it doesnt matter how much people are spending, but to be a fundimental part of a mechanic.
I dont think FeH is very P2W, I am completely free too play and although I struggle staying in tier 20 sometimes because I still lack some merges. I dont find myself struggling with whales too often, and I personally take pride in defeating blatant whale teams with my completely F2P team, the fact that someone payed 1000+ dollars and I cant defeat their teams is not a feeling you get too often.
Overall I think FeH is in a pretty good spot, sure the T20 score is much higher because of the whales out there but overcoming that is much more satisfing because of that. While the game is in a state that paying gives you an advantage its not an advantage that is exclusive, since +10ing units isnt impossible for F2P players, the mechanic is P2W but overall I prefer it that way since its not at a point that F2P cant overcome it