I'll just leave what Imotekh said to Marshall Helbrecht: "You have ruled this galaxy for ten thousand years, yet have little of account to show for your efforts. Such failure must be as depressing to bear as it is pathetic to behold."
Just look what the Necrons achieved during their times: Being enslaved by higher beings because they were too stupid to advance enough on their own to win the war against "The Old Ones" now that is just sad, Necron-fools
Yeah, then Magos Telok will just use that energy to reverse time, or some random technobabble that achieves the same goal.
Because you Necron are too scared to face the Great Devourer, we at least FACE them... Not to forget we at least have guts not like the genderless Necrons