First, I respect your objectivity as a Cowboys fan to include a Cowboys team as one of the "finalists" for this dubious honor.
Second, just wondering why there are no teams on this list prior to 1971. There were around 40 seasons of professional football prior to that year. Can we say with any certainty there were no dreadful teams during this almost four-decade period? Perhaps we need to be football historians to know for sure, but although I have little hard data to back it up, we should include the 1958 Packers on this list (who happen to be MY favorite team!). This was the year before Vince Lombardi became head coach. I recall this team only won one game, and was so lax, the coach actually played cards with the players!
But I degress. The teams on your list all have a claim to "the title" (I don't think we can evaluate teams solely on their record, so we can't claim a team is better than Detroit simply because they won one lowsy game).
But my choice would be the 1976 Bucs. Sure, the uniforms that looked like Creamsicles didn't help, but totally apart from their record, this was a team that was truly inept. It's not a knock on their coach (John McKay, who was highly successful at the college level), but was a classic case of the "first-year-of-existance blues." A new coach on a new team with new players (most of them cast-offs from other teams) who never played together before is a recipie for disaster in a competitive league like the NFL. And having the opportunity to actually watch this team in action on occasion reinforced my belief that they were doomed from the start. To have even one victory that year in my view would have been a grand accomplishment.
Gotta give the team & their fans credit, though. They hung in there, eventually established themselves, and eventually made it all the way to Super Bowl champs! So I'm not knocking the Bucs or their fans in general - but that inaugural year of 1976 was just something they all just had to endure.
Thanks for the stats. You gave us good reminders of some teams we might have overlooked. And isn't it encouraging that most of them eventually became World Champions? Hang in there Lion, Saint, and Bills fans -- your day will come someday!