>>64383101
While generally true (chaos ships are often Great Crusade era ships) you have to remember that a lot of the times they are also in terrible state of disrepair. When systems break they have no way to repair them into previous high tech tier, and have to ghetto-rig some alternative that is usually crude and inefficient.
Like the famous picture of "the Macro-cannon autoloader is busted, so we'll just use a thousand slaves to operate it manually". Or if some engine is broken, they'll just make a big-ass hamster wheel and have slaves churn it 24/7 until their legs break. Tech is difficult and expensive to make, but you can always have more slaves.

Not that the Imperium would be much different, they too will absolutely go for Smekalka-type cope technology if they have no other option. But usually the Imperials have better access to quality materials and shipyards, so they tend to have things a bit better, even if it's not Great Crusade era gucci stuff.

Also, occasionally chaos ships can have much more unorthoidox and weird, wacky tech, because the dark mechanicum isn't as afraid to experiment and try new designs (or just bolt on some tech stolen from aliens). So their ships may have some exotic weapons systems or other configurations.