Actually D3 is rife with dynasties. UMU is a good one, but not the most dominant. You'd have to look at Kenyon swimming or the two schools that have dominated wrestling for much longer than UMU let alone UMU/UWW dominated football. Messiah is ridiculously good at soccer, a sport where thanks to low scoring good teams lose to lesser opponents at a much higher rate than sports like football. Some of the women's sports are even worse.
Well, wrestling's a bit different because a team can have multiple individual national champions even if the team doesn't win one. Ithaca had that happen a year they finished 5th as a team.
I think football is a unique for reasons I've mentioned before: It isn't just the national titles, it's that, with Mount specifically, they're almost always going undefeated before the Stagg Bowl and are routinely just blowing teams out every week. As was posted earlier, 46% of their games since 1996 have been won by 40+ points! And that's a pretty high bar for uncompetitiveness, IMO.
Look at this stretch in 2012: 57-0, 52-0, 54-0, 66-0, 62-0, 51-0. There's a level of complete and utter dominance that goes beyond "Mount wins all the time". Whole sections of the season are mere formalities. You might as well not keep score.
I don't disagree, I'm just pointing out that DIII dynasties aren't limited to UMU or the UMU/UWW pairing. It's fairly common. Baseball and basketball seem to avoid the issue, but most D3 sports have long stretches of single team dominance. I'm not sure what UMU is supposed to do about the rest of the OAC. They simply can't make Marietta better. They aren't going to move to a new conference since the OAC is a good spot for them for all sports.
W&L has won 23 of the last 25 ODAC women's tennis championships, losing in 1989 and 2002. The team started in 1985/86, a year after W&L went co-ed. The men's team has won 32 ODAC championships since 1977, the year they joined the ODAC. So 32 of 38 roughly (counting this year). But leaving the ODAC in all sports to find better competition in tennis just doesn't make sense.
Football is a flagship sport, but the realities of the problem exist for a lot of teams in a lot of conferences. There just isn't much you can do.