I'll post on this in detail when I think of it... just jotting this down for now. I think I came up with a way for a dg to win 100% of the time after 7-10 minutes playing on the typical bobby filthy rich settings. This isn't me taking a shot at bobby at all, btw. I just want to show that its somewhat futile to play on those settings and I'll suggest an improvement afterward.
Update:
So, I ran a few demo games using less than optimal builds. First, here are the game settings I used. They are either spot on or might be off on flag capture duration - can't remember.

These settings are typically used in 3v3 and > on Exile (primarily due to location of the artifact shops, I'd think)
Here are the replays:
http://www.box.net/shared/agk3yeq2ta
http://www.box.net/shared/fgt4dktabm
Each game ends a little after 10 minutes with me destroying the enemy citadel.
Basic strategy:
Play as oak - stay in a lane with creeps as long as possible. Generally, while the other flags are contested, you'll be able to stay in a lane without too much issue. You don't really need to be all that aggressive - just make sure you are leveling. I chose a heavy damage kit, but frankly, as you aren't going to be fighting other dgs much (as possible), as long as you pick up treads and stack some armor, you'll be fine in most cases. Pick up last stand at level 8. Run through the high towers, shielding as needed. Pop a sigil when needed. Get up to the citadel and start pounding away. You'll die, have last stand activated, then die for real and come back after like 5 seconds due to the light death penalty. You likely just did about 40-50% damage to the citadel. Teleport as close to the cit as you can and repeat. Just do this over and over and over. Even if everyone on the other team starts to try to defend against you, still have shield + sigil, which buys your some time (and as you only have to make it to the citadel, that is that). In short - if you reach the citadel before last stand is activated, you'll destroy the citadel after 2-3 runs, tops.
Flaws in the setup:
The light death penalty is fun as you get right back into the battle. Not so fun if you have a dg like oak that, when he dies can do even more dps and be completely invincible. Oak's just a basic example, though. You could accomplish the same thing with a ub or many other dgs without much of a problem.
So, how can you counter this sort of thing? You can't really. The low war score rate and high xp rate means that by the time I hit level 8 or so, neither team will likely even have ws3. So, you can't upgrade the strength of your citadel past fs1 (not that it would help much). The only way you could try to buy some time would be with mass universal gadgets... and if you are wasting time doing that, I'm already on my way back to work on the citadel some more. Basically, the moment it dawns on a team to rush the other teams citadel, the game will effectively end. Each and every dg can do a ton a damage. As long as you reach the citadel and start pounding away, the game will end.
Suggested changes to the setup:
It seems like the biggest flaw in this is in how easy it is to kill the citadel. Now, I noticed that the folks that play this alot didn't really bother with citadel rushes. Instead, they were extremely aggressive towards the flag control aspect and focused on PVP much more than taking out towers, etc. Based on that, I think a really simple change that would take away the easy kills on the citadel (not completely, but in a huge way), would be to play these games on dominate or slaughter. Seems like that's what the folks already playing this tend to enjoy doing anyway.
Here's a short replay of me using the same tactic, but with the settings on dominate (in case you don't know, on both dominate and slaughter, you actually take damage if you attack the citadel and the citadel has substantially more HP at level 1.
http://www.box.net/shared/hrlt9ylgzj
Anyway, if you bothered to watch, you could see that, while I was still able to rush the citadel, I would not be able to take it out quickly, even with the quick death penalty. That's not to say I still couldn't do it, but with the change in game type, the other team would have a chance at defending.