I'm pretty damn sure the Moloch incident with big E was told by a heretic rather than being explicitly written.
No. It was Alivia Sureka, a perpetual and one of most trusted people to Emperor. While she didin't went into the gate with Big E (which is why we don't know how exactly did the Emperor achieve it), she was later left behind to guard it. It also checks out with heretical sources because hell, if the Emperor didin't actually dicked Chaos Gods over they surely wouldn't claim he did. They're mad.
Also that would be pretty fucken impressive foresight of the Necrons, since 60mya even the earliest known ancestor of primates wouldn't exist for 5 million years.
First line. Also, yes, I agree it's retarded (and would imply that ALL the primates have it, GORILLA CULEXUS WHEN) but it doesn't really had to be Necrons themselves, just the C'Tan. And yes, it's questionably canon but as long as it existed and was never explictly proven otherwise, it's canon.
Over the 38,000 years between now and 40k, humanity has evolved from "basically non-psychic" to "basically low-level psychic". The supposed insertion of the Pariah gene into random early mammals would have been pretty much random, seeing as that was a period fifteen hundred times further removed from modern day "basically non-psychic" than "basically non-psychic" is from "basically low-level psychic".
It wasn't evolution. Humanity was non-psychic because the sacrifice of Shamans and creation of Emperor effectively removed psychic abilities from humanity for long, long time (either because >Warp shit (more proable) or because he basically used up all the people with psyker genes (more scientific but doesn't exactly make perfect sense because psykers don't work this way)).
Sometimes fluff is retconned not because of the power lance up GW's ass, but because it's fucking moronic.
SQUATS.
Edit: Let's suppose that Modern Humanity's ambient level is 100,000 Arbitary Units of psychic, and that the Imperial Humanity's is 10,000,000. If you assume a linear progression (because what the fuck is there to compare against here?), then the level of psychic activity in the pseudomammals that the Necrons gene-edited would be 1.0x10^-1496 Arbitary Units.
Obviously this calculation doesn't mean much because it's based entirely off of Fermi estimation ("This seems about right") and the Emps had a big influence on how psychic humanity was, but the sheer orders of magnitude involved here show just how fucking stupid an idea it was. In fact, the Imperium being only about 100 times more psychically active than modern humanity is probbably a huge under-estimation.
Modern Humanity's ambient level is proably usually between Pi and Psi which is... between 10 and 0 Arbitary Units of Psychic. Imperial Humanity is... between Pi and Psi usually, which is between 10 and 0 Arbitrary Units of Psychic with rare exception of Psykers which are between Omicron and Gamma which are about 1000 Arbitrary Units of Psychic and 100,000,000,000,000,000,000,000,000,000,000 (made up but you get the idea) Arbitrary Units of Psychic. You're taking Humanity as a whole while it simply doesn't work that way - there is more (and more powerful) Psykers but the general population doesn't get more psychic.
As for the actual Omega level Blanks, they have... -1 Arbitrary Units of Psychic because it works like this - either you're a Psyker who has some weird connection to Warp with their soul which makes it bloat, or you're normal and have bigger or lesser "soul" (and the lesser it is, the more resistant you are to Warp) or... or you're a Blank and simply don't have one. There are no levels of Blank, because there is simply nothing to measure. Of course there is still Omega-minus level, but that's quite different from regular Blanks because they're literally antisoulmatter (as opposed to Blank lack of soulmatter) which makes them ridiculously deadly to even regular humans.
Also, as far as I'm concerned an awful lot of people carry Pariah gene but not everyone has the dominant version and is a blank. Hell, it might be actually the sole reason why humanity is not yet all Psykers.
https://www.youtube.com/watch?v=PzsDLpNMZq0
Yes please.
After watching this I literally cannot contain my
LOYALTY.
At least they don't wear somberos like the last time.