For a team in a single season, I'd be hard-pressed to find one that was more dominant than the 1985 Chicago Bears. They went 15-1 in the regular season, then ran through the playoffs with three victories by a combined score of 91-10 (with two shutouts).
They were #6 in total offense (#2 in scoring offense), #1 in total defense (#1 in scoring defense), and had about 12-15 Pro Bowl caliber players on their roster. And all the silly nonsense surrounding William (The Refrigerator) Perry overshadowed the fact that this may have been the finest defensive front seven ever to play in the NFL.
You do have an argument with them. If you expand the "team" to include coach, I think those bears beat the 1972 Fish 7/10 times. But you never know. In the Dolphins undefeated season, people forget that one of their closest games was a 14-7 victory over Dallas in Dallas . . . and that Roger had torn up his knee that year and we had Craig (ugh) Morton. A Staubach-led team would have won that game.
Much of the Bears' strength that year was NOT just their terrific defensive players, but a radical defensive scheme by Buddy Ryan that the league had not caught up to. If you notice, however, the league did catch up to it pretty quickly.