Free or not isn't the issue here. I'm by no means a free player, and I'm still fucked over in this event. I refuse to spend hundreds just to get this event's reward. I've already spent more than I should have.
I've spent 20$ on this event alone. Any other game I've ever played, that would be more than enough to ensure you get all event rewards that were not gacha only. And yet, I'm still so very far from the kill counts required. Because I hit them with wet noodles after my slayers cards were taken away early.
It's TOO EARLY for these huge ass bosses when we are required to spawn or get the killing blow for credit. I have 11 thus far, and I'm active as long as I'm not sleeping.