All of the factions in base are ridiculously OP if you play them right, but the Consortium is by far the most OP. They can get cap ships earlier than anyone else (and build them faster), their basic bomber is basically a slower B-Wing, they can acquire ships from other factions through piracy (ever tried dealing with a Consortium player who has B-Wings? It's not pretty), their credit income is leaps and bounds better than anyone else's, they can destroy your structures without even invading, their space stations build much faster, they don't have tech levels, their heroes can stealth and are all incredibly powerful, and their ships are really strong too, did I mention the defiler's bomb is ridiculous? There's no way to avoid it, it can be placed anywhere, it does huge damage, and has a large area of effect. Their bombardment is easily the best, all their structures have shields, etc.
The Keldalbe's shield drain is ridiculous, and as long as the Consortium player has some gunships in there to pick off bomber spam, you can't knock out the hardpoint, because they can intercept torpedoes with point defense (only faction that has this capability, not counting the imp's juggernaut, that's a land unit nobody uses because it sucks). Plop down some buzz droids with your starvipers and watch them decimate enemy fighters. The Vengeance (idk, whichever one can cloak and has no shields) can cloak and blow up in the middle of your fleet. I could go on, but I want to get into land units.
On land, you can't touch a halfway decent Consortium player. Their buildpad structures are the best, the mass driver can kill almost anything that isn't a heavy vehicle very easily, and the proton thing can do the rest. The Canderous tank is probably the most overpowered land unit in the game, just spam these and watch your enemies die, seriously they're good against everything. The droideka is better than either the T-2B or the AT-ST in almost every way, except hull strength, which is easily compensated for by its obscene firepower and incredible speed. The Grenadier squad, while short range, has WAY too much firepower, it can easily kill even jedi heroes in numbers, and decimates other infantry. The Merc assault squad is fine at first, until you give it disruptors, which no sane Consortium player would not do. They make swiss cheese of any other infantry, and even just 2 or 3 companies can destroy an AT-AT or a T-4B in a matter of seconds. Their artillery unit is by far the most agile and durable, and while it hasn't got as much firepower as the others, it makes up for this with its carbonite missiles that slow you down, and its good range and rate of fire. Tyber can bribe and stealth, urai can neutralize infantry and tear up all but the most powerful vehicles in seconds, and is a worthy opponent even for the most powerful force using heroes, Silri can wipe out a group of light tanks and infantry just by pressing drain life, and her rancor can take care of most large things. The Vornskr is incredibly fast and really good against infantry and heroes.
The Nightsister Rancor is agile for a unit of its power, and while not as durable as a T-4B or AT-AT, it doesn't need to be. If it gets in close, which it can quite easily, you can say goodbye to your heavy units because it will kill them very quickly. I'm not really sure about the ewok handler because I don't use them much, but I can easily see them being overpowered too. Did I mention you can spam defiler armies which can stealth past any space defenses? They have 2 bounty hunters, allowing them to easily eliminate any heroes which might be a threat to them at a planet they want to attack. How could I forget the pulse gun tank? Get a few of these and pair them up with some canderous tanks and infantry or droidekas, and you are basically invulnerable. Oh, and even if you do somehow manage to lose, its okay, you can just blow them up and take half the enemy army with you! Bossk isn't that great on the ground compared to other consortium heroes, but is still very powerful. IG-88 has tons of AoE damage and can shoot you with his fast firing, very powerful blasters from long range, and is also very very fast.
Oh, I almost forgot, the M9-TZ transport, while unarmed, doesn't need to be armed! Just load this thing up with your heroes and some merc troopers with disruptors, and drive right past all your enemy's defenses! Then unload them, blow up power generators, turbolasers, and factories, and call in a bombing run and your bombardment, which is the best, when they come to retaliate!
The Consortium might be fine if you're fighting the AI, but if you're fighting a player who has ANY brain cells at all, you don't really have a chance. I played with my friend who is about equal skill level to me, with me as Consortium, and even refusing to use Sabotage and some of the consortium's other most overpowered tools, it still wasn't a fair fight, and I ended up blowing up most of his fleet using Hack Deathstar when he got the Deathstar and was taking it from planet to planet with a "doom fleet".
Note: Some of these conditions do not apply to skirmish, skirmish is more balanced, but the consortium is still overpowered.