Cre is a momentum trait. If you let him live too long, he'll cream you no matter what. It's a good trait for a huge galaxy. Do you recall the galaxy size, and what the turn number/stardate was when these engagements started? Because you can basically kill a Cre player in about 100 turns starting from pre-warp, unless the galaxy is very big and empty (in which case you should consider taking Cre also).
In a smaller map Cre will always get killed by an early rush from a non-Cre. Cre is expensive and there are plenty of profiles that allow a faster early game. Standard procedure in past moo2 games with a lot of humans in them was to dogpile anyone stupid enough to roll it. The strongest are UniTol (industrial race) and DemoLith (tech race). If I had to characterize these:
1. Demolith seems to be the fastest. My best date for killing the orion guardian is ~t125.
2. Unitol has the best midgame, by far.
3. Cre has the best end game.
Tactically, a venerated strategy is to use the 'missile boats,' a player term for ships laden entirely with 2-shot missile racks, to just blow up his ships as they approach, since they have to get right in your face to board. May as well make use of that. 2-shot missile racks pack more destruction per unit of space than anything else; battles are quite brief.
The opportunity cost for pursuing the chem tech path for merculite missiles is zilch, since you will be needing armor and pollution techs from this line as well.
The opportunity cost for getting scanners (reduced missile evasion for enemies) in the physics line is either the 250rp battle scanner (not recommended to skip battle scanners) or the 900rp neutron blasters, which are at cross-purposes with a missile strategy.
The simplest, most direct way is to use neutron blasters as your beam weapon of choice. Neutron blasters kill marines at a rate of 1 marine for every 5 points of damage that penetrates the target ship's shields, so even if you only inflict a couple of hundred points of damage, you'll still kill every marine on the ship. The only tech that blocks this effect is Damper Field, which is an exotic tech that has to be either discovered on Orion or salvaged from Antarans. Failing that, there are a couple of other things you can try:
- Think about investing some racial skill points into ground combat, so your ships will be harder to capture. You can also research a few ground combat techs yourself. (This still won't defend you against neutron blasters, however; your marines can't fight when they're all dead.)
- Research security stations. They're expressly an anti-boarding tech.
- Research at least one shield tech. Ships almost always need to have their shields down in order to be boarded (except in the case of assault shuttles), and some defense is better than none. You can complement any shield tech you have with shield capacitors and/or multi-phased shields to make them harder to bring down.
- If you have shields, research hard shields. They'll block transporter beams even when your shields are down.
- You can try to turn the tables on your friend. Combine the neutron blasters above with transporters, and you can capture enemy ships with relative ease (this is probably what he's doing to you, as ships generally don't advance far enough on the combat map in their first turn to capture anything). You can use transporters to recapture ships that he's taken from you (since the marines on that ship will probably be weakened), and if you're a telepathic race, you can use captured ships in the same battle where they've been taken in order to help your chances.
- As a last resort--and if you have access to the tech--equip your ships with quantum detonators. Any ship with a quantum detonator has a 50% chance to explode upon capture, which is partly why Antaran ships are so hard to take.
Security stations come at the expense of offensive equipment which is necessary to win battles, so this is a hard sell. Technologically they come at the expense of neural scanners, which are handy in preventing Cre spies from blowing up all your starbases.
Ground combat investments have the same sorts of cost in terms of tech and racial traits. Honestly you just don't want to get into late-game ground scraps against creatives. You just use your early 50 turn lead in tech and ships to annihilate them.
If a creative is being allowed to research 2750RP techs like transporters, they are being allowed to live wayyyyy to long :(