Remove genetic things from lings entirely.

[DJ-Fireball_did_this]

Then we have to do the same for Vampires and Werewolves...also do not forget Vampire Thralls (which are Zombies...so...which WERE human in the past).

No, you don't. Stop conflating the two. Vamps and wolfies are both a great deal closer to humans than lings are. They use oxygen, are bipedal, mammals, have a spine, a single center of symmetry down the middle. Wolfies are also a terrible example since upon transformation they lose an assload of normal crew gear and will probably not get it back. They're limited in a much similar way almost permanently.

You make them different by substracting stuff that they can choose to do? Does not make sense to me,...

...yes? Genes are a thing traitors can use. If lings couldn't, that would be a difference. Yes it's a choice to act functionally identical to traitors but c'mon, they always pick it. Lings not just looting for human weapons and shit are almost rare.

You could also give every traitor the option to buy a device that makes them into a ling. Or give every uplink access to every job's syndicate items. Those would be choices but they'd still suck and destroy the difference between antagonists. Making something a "choice" doesn't inherently mean it will cause diversity or not do the exact opposite.