No way did they have 15 capitol ships in 20 minutes, unless it was 5v5 and the other 2 people fed every last resource to them.

They attack the weakest because that is strategically sound.  If there's an underhanded way to win the game(Like bomber spam)  people WILL ALWAYS USE IT IN ONLINE PLAY!!!

just the way it is.  Not to say there aren't good people to play with online, you just have to learn all the dirty tricks they use.

Game balance is also a big factor.  Right now, Carrier and Colony capitol ships should always be your first 2(Not necesarily in that order)

-Twilight Storm

-Twilight Storm

It'd take five players each building three capital ships to have any shot at having 15 within 20 minutes, and even then they'd be too far away to coordinate their attack.  This is, for all intents and purposes, impossible.  In terms of online play, if you're on the front line in a large team game you will be attacked by the full force of the enemy team.  This isn't them picking on you, this is just them attacking the nearest available enemy.

Part of your job as a front-line player is to be aware of your surroundings and react accordingly.  If the first you see of a large enemy strike force consisting of multiple players is them bearing down on your planets, it's already too late.  You need to be proactively watching what they're doing and preparing for it.  If you're going to take a 2v1, you need to ask your allies to give you money.  If they can't afford that, you hunker down with a starbase and prepare to weather the storm.  If you get blindsided by a sufficiently powerful attack, that's enough to defeat you right then and there. 

Reading this, I don't completely understand whether you mean you were attacked by 3 AI opponents ("people") or by actual human players in online multiplayer.  In online multiplayer, sending 15 capital ships and all of those other ships out to attack one single player with a tiny fleet in seems like a horrible strategic choice simply because doing that would make them wide open to attack from your allies.

Was this game against the AI on one of the hard difficulty levels, such as Unfair, Cruel, or Vicious?  I could believe that because the Vicious AI (4x economy bonus) gets insanely large quickly.  If this game was against AI, were the teams locked or unlocked?  If the teams were unlocked then it's possible that the AIs allied with one another (which they will eventually do) and ganged up on you.  (At least in regular Sins and Entrenchment it would do that if you didn't set it to Locked Teams.)  So, if you're playing against AI, try it with Locked Teams to force the AI to fight one another.

If you're playing this online against real human opponents then don't play unlocked free-for-all (FFA) games.  Instead you would be better off playing locked team games where the players normally end up matching up against either other 1-to-1.  (Worst thing that could happen to you would be if you started out in the "suicide" spot between 4 opponents with two on each side; in that case, prepare for an early 2-on-1 and consider sending a colonizer capital ship to the middle of the map so that you can migrate if need be.)

the most enjoyable way to begin your adventure with SOASE is to start with a 5 player game, a 2v3 with you&two allied AIs against two other AIs. Set all AIs to normal or hard (either way, you shouldn't be getting too much attention). Lock the teams.

If you have entrenchment, research the starbases and plant one or two in chokepoint locations (remember to upgrade them - 2 offensive + 3 defensive with repair bay support ought to take out any early-to-mid game invasion). If you're not Vasari then remember to build all your structures around the starbase and get some hangar bays or carrier cruisers for fighters (to kill siege and assault frigates/cruisers - the ones that bombard the planet and the ones that snipe structures from afar). And repair bays - repair bays are the best thing since sliced bread, at least in the Soase universe (make sure you have at least three next to your starbase, their areas of coverage overlapping). AIs suck at taking out starbases, so you should be doing a fine defensive job while your allies keep the pressure on the enemy. You'll see some nice battles going on on the map, make sure to watch them. Watch how AIs start, how they take their planets (you might even add one Unfair AI in your team, unfairs are much more interesting to watch than normals ).