Marathon matches have different dynamics. The removal of the time limit means you can no longer win by score, IE a 30 minute siege will get you no where. People need to understand that you have to be aggressive on marathon servers, which is part of the problem. People *don't* understand this, so the matches takes ages to finish. Take the 5 mammoth tanks you have firing ineffectively on that Hand of Nod and move into the base to kill the obelisk, or take an apc or two full of people and somewhat suicidally rush a building.
You don't have to be so aggressive in standard servers because you *can* win by time limit, so people take those tactics and those strategies into a marathon server and waste everyone's time.
For future reference, all of the "pro" players prefer AoW because it's the standard used for pretty much any competitive shooter, timed matches, not because it's an innately better mode. The "pro" players understand how to get things done in Marathon matches just as well as AoW matches.
Neither mode is better or worse, or more competitive, when played by people who know how to handle each mode. This entire discussion also has basically nothing to do with the OP.