Grey Knights were decimated banishing Angron for a time. After that the Inquisition planned to kill/lobotomize all the millions humans nearby. So yeah, whatever number of guardsmen will do, if some survive they will be killed by the Imperium either way.
It’s been done. Whether against Angron or not, I have no idea, but the lore and attrition tactics go together like pb&j
Grey Knights were decimated banishing Angron for a time. After that the Inquisition planned to kill/lobotomize all the millions humans nearby. So yeah, whatever number of guardsmen will do, if some survive they will be killed by the Imperium either way.