People will always be salty about things you save up for. I was playing a F2P account just to see how long it could take to get the latest ninja that came out (Tobirama Edo Tensei), got it within 4 months of spending all my coupons only on him. Take him to arena and within 4 games get called a P2W scrub (literally him, water main, jinpachi, and darui).

Dont pay them any attention, its not worth it. At this point, the only pay to win ninjas in the game are the Ronin Naruto, 10 tails madara, and 10 tails obito. F2P people can get any other ninja in the game at a reasonable rate if they are committed to getting them.