>>96804064
The worst quality of the Black Library reader is to take ever bit of wank and integrate it with suredness of fact. Really put on your thinking cap for a second, if all they need is test subjects why can't they just keep Truman Show style colonies under their thumb after eliminating the irritation, if it were so easy? The answer is because the point of the setting is to sell toys.

The tyranids can make acids and diseases so aggressive and virulent, according to fiction that means to portray them powerfully, that they can eat through power armor and choke plague marines to death. They could semply send assassin fleets of acid gaunt bombs to every tomb world. So my super laser beats your laser shield and it is me who could destroy you at a whim (I choose not to because I am savoring the flavor of my lunch).