We've already established that your dogma about the Assumption of Mary is based on one word, so the real strength of this position lies with your church fathers. How do you know they got it right?
Your church fathers were fallible humans. They came after the fact. We really don't know if the few that actually knew the Apostles really understood what was being taught. None of their writings have ever been treated as inerrant.
No one will argue that certitude regarding the Assumption of Mary is not to be found in the patristic evidence. However, the subject was discussed by some of the Fathers, with various opinions. For example, Epiphanius (c. 377), questioning the possibilities of Mary's end, states: "...or she remained alive, since nothing is impossible with God and He can do whatever He desires, for her end no one knows" (Panarion, 78, 23). Augustine says Mary died, whereas Ambrose says he is not sure. The mere fact that the demise of Mary was even being discussed, which was not that case of any other New Testament person, shows that, among the Fathers, something was different about Mary.
John Damascene in the seventh century (Second Homily on the Dormition of Mary) seems to give clear evidence that Mary was assumed into heaven. John Damascene wrote during the era of Byzantine liturgy. Also during this time is St. Germanus of Constantinople (d. 733) and Modestus, bishop of Jerusalem (d. 634), who teach that Mary was assumed into heaven. Also, in the Sacramentary of Adrian I sent to Charlemagne, Mary's Assumption is affirmed. Prior to these witnesses, Theoteknos, Bishop of Livias in Palestine, from the sixth century, affirmed the Assumption of Mary in four separate instances.
Epiphanius' fourth century question about Mary's demise was still unanswered in the 20th century. As the centuries pass, there is a constant question, one that will not go away, of whether: (a) Mary died, and (b) Mary was assumed into heaven, with no dogmatic answer to either. The question did not cease up until 1950. At this time, it became a consensus that Mary was indeed assumed into heaven. Finally, in the late 1940's, Pius XII wrote to all the bishops of the world and asked them their opinion. 99% wrote back and said they believed that Mary was Assumed into Heaven. Here is a perfect example of how the Church's bishops, in union with the Pope, fulfill the statement in Matthew 18:18 concerning their prerogative to bind and loose.
1 Timothy 3:15 says "the Church is the pillar and ground of the truth," which is, of course, a timeless truth. The dogma is the arbitrary result of the Church's authority, not the result of the preponderance of the scriptural and patristic evidence. Since Scripture is not the final authority, the Church wins.