I was partly referring to just making that powergamer suffer through 8 levels of his build being worthless (and maybe dying). But yeah also that. 3.5 & PF made multiclassing a bit too powerful.
I have multiclassed only a couple times. the most notice two:
You can literally just give your crew a space ship. This is very common, apparently. Or it's on perma-loan from your "patron". If you're going to do that, make sure your ship barely has any cargo space or empty staterooms. Spaceships are money making machines, if you have no debt, you effectively have unlimited cash. The debt forces the crew to constantly be moving between systems. If you want to make your stuff less lethal, there's a Luck systems in the Traveller Companion. Been looking at the 2300AD books and treating it like another Supply Catalogue book, the gun designs and general aesthetics are better.
The best way to make a Gish / spell sword type character has been one point in warlock for the last one and a half versions of DnD unfortunately, so I've had to quite a bit.
Not surprising since 2300 started out as an attempt at harder military science fiction with the Traveller ruleset back on the day. It's also a sequel setting to Twilight which GDW also made.
I've only played Mongoose, so take what I say in that light. You can randomly start with a ship and a shitload of money. Or you can start a broke-ass nigger with no friends. It's very swingy. However, once you get into the game, the economics are just flat-out retarded. If your ship takes a hit in combat, any hit at all, it's very likely that the repairs will be so expensive they wipe out all of your profit from the haul. The campaign we were doing basically died after we had loaded our ship down with a pretty good haul, ran into a pirate, took one hit, and the repair cost table wiped us out. The GM insisted this made sense "because space ships are expensive," but no, it doesn't, because if shipping involves significant hazard, shippers will charge more.
There has been a decades long debate as to whether space piracy even makes any economic sense within the setting and established rules, and within the Third Imperium's space, there really shouldn't be any at all, given the safe free trade zone offered by membership is kind of the whole point of the thing. Especially not the shoot first, ask questions later type. Really the pirate should have first held you at gunpoint and demanded you drop some cargo or pay a ransom, then shot. Because any encounter a ship couldn't just jump from directly, would be well within system defense boat range, and getting shot up isn't fun for the pirates either.
Which is how most piracy operated in the Golden Age of Sail unless you were proper, credentialed Privateer.
"The space combat rules are actually window dressing; GMs should know better than to ever actually use them," just confirms it's a bad system. Systems that break the game if you use them are bad systems.
Get Greyhawk Ruins off Drivethru RPG and just run it.
That's like saying the combat rules for Call of Cthulhu are bad because they're extremely lethal, as if that's not the point? The danger and expense of space combat is a threat itself and a risky undertaking to all involved and best approached as one-sidedly as possible by the initiating party. It incentives approaching the game in an authentic manner, it's not profitable to risk your mulit-megacredit ship on a few k worth of cargo or bullion ransom. Similarly, being gunned up or protected by the authorities will make it just as unprofitable for pirates to try to take you on.
What the hell was the ship made of? Bonded superdense with high tech stealth plating? Repairs are expensive, but unless your ship was some top of the line shit, it should be affordable. Just sounds like the numbers were fucked with more than anything. What ship were you flying? What weapon hit you? A standard freetrader, while expensive, itself is worth only a few megacredits. The more I've learned about this, the more I'm convinced your referee was being an idiot.
The Pirates of Drinax campaign book explicitly lines out that you should operate exactly like that, multiple times, drawing lots of analogies, and has your boss tell you to run a protection racket, not a mass murder scheme.
Recommend you start them with Tomb of the Serpent Kings. Its a good "baby's first OSR" complete with encounters and rooms set to teach specific adventuring lessons. If there's a failing, its there isn't a particularly srong incentive given to explore said tomb and you need to BYO.