You gotta look at it from the games standpoint. You want edo tensei easily, some want susano itachi, others in future want madara&kurama naruto....

Look at susano itachi: a ton of f2p players complain how they will almost never get him

Now think of the boxes, wheel,etc as a lottery.... if you pay for a ticket do you expect to win? No you try and hope. You can waste 1,000,000$ Usd on 1$ tickets for a chance at 1,000$ *lol* and all 1million= losers not a single win. Just as they have the same odds of all 1million being losers they have same odds of all 1million being winners.

Now as you see from that example same thing goes for game. Even if the odds were 99% chance to say get a hashi in every box, or a edo deidara in wheel still a chance to not get either regardless of how many coupons invested.

So in short its fairly set up. Did i get a edo deidara? No i have not. Did i get a raikage on wheel? nope. Even so doesnt make it unfair, just unlucky. Best bet try&hope but dont let it get you down :P