Sorry for replying so late. (I had to go sleep)
Sins has it's own flavour and turning it into poor man's starcraft would just ruin the experience. Quick games=lack of strategic depth or very high emphasis on micromanagement. You just can't think and/or input commands fast enough to materialize more complex strategic ideas, which is reflected in game design. People ar not AIs.
Well, I don't like games like starcraft too...my favourite game was "supreme commander FA", which unfortunately has been turned to something too simple (supcom2).
Actually, once it's clear which team is going to win, the players on the losing team call it "gg" and quit.
I don't think that's so good, I don't like when people (I am talking about other rts games) say gg and quit, when it's clear I am going to win I want to crush ALL your empire.
If you show a 5v5 replay (a good one) to a friend of yours (who doesn't know anything about soase), I am sure he won't understand who won...(even when they say gg)...but I am sure he would understand everything if you showed him a starcraft replay...
The point is, if I don't understand the game I just won't buy it, even if that game is much better than something like starcraft.
Why don't you log onto Diplomacy sometime and try a 4v4 or 5v5 game? Maybe you'll like it.
Unfortunately I was able to do that about a year ago...now it's very hard to find a game... 
The only games that last "way too long" are those with overly tight choke points. Otherwise games that last longer than 90 minutes are uncommon. That's probably still too long, but not "way" too long. I think Sins has very strong multiplayer, but it wasn't able to hold on to a large multiplayer community.
I don't mind if an epic game lasts 2 hours, I mind if you have to play, let's say, 60 minutes and then you find that game was not so good.
The games are (potentially) very long but the fact that you can save and restart them is absolutely one of the most brilliant features ever put into a game like this. It's what makes Sins unique in a huge way and I it's what got me--the guy who doesn't have loads of time for super long, uninterupted online play--to buy it in the first place.
I like that feature as well, but I think that in a 5v5 game it is not so worth it to save the game...(it'll be hard to find those people again and in the same time)
But it's still a nice feature you can use with your friends! 
Thank for your answers and sorry for my english! 