According to any Christian Jesus died for their sins. According to any JW Jesus died for Adam's sin.
Who knows if anything in the Bible is true or actually happened? However for arguments sake, JW's believe Jesus death or ransom sacrifice was intended to buy back the life Adam and Eve lost for us, (their descendants) who inherited their sin.
It's a case of which came first....the chicken or the egg?
Adam and Eve's disobedience was the reason that the sacrifice had to take place and they are the reason we inherited sin and why we need Jesus sacrifice. He could have said "no way" but instead because of his "undeserved kindness" he allowed for this provision.
JW's believe Jesus died for both Adam's sin and their own inherited sin. But...they believe Jehovah is the one who allowed the life that Adam and Eve lost, to be bought back via Jesus sacrifice.
They fully honor Jesus and the sacrifice he made BUT they realize that had it not been for Jehovah, none of it could have happened.
Whether or not humans think it was unfair of God to punish everyone for what Adam and Eve did, is unimportant to JW"S. As the Creator of the universe, they feel he has every right to handle things any way he wants.
I might think it was dumb that a god who can do anything, created us so that we need food and air to survive. Why didn't he just create our bodies so we wouldn't need those things or so we didn't feel pain? A JW believes that we have no right to question the way god does things and whether or not we think his ways are fair is unimportant.
They believe that Jesus is important but without Jehovah...there would be no Jesus...no nothing....so they view him as #1 but that doesn't diminish Jesus sacrifice in their eyes.