I am not a mod, but since you want someone telling you "No, you're wrong", I might aswell take upon such a duty myself.
You can obtain Sasori from this event.
First and foremost, it is not impossible. An extremely low chance is STILL a chance. You just showed us the maths for it, so unless you are saying your maths, and thus the point upon which you're making your argument, are wrong, I don't see why you're complaining.
Second, and just as important, they never claimed you would obtain 80 fragments. You can obtain a ninja by getting the last 5 fragments you needed, for example.
You're just making it sound like you're being deceived because the truth is not as you wanted it to be.
I am surprise Daiske and Yuusuke are putting up with your attitude to be honest.