As far as searchlights make NF a non-issue, I'm not sure what the Necron player is doing, but even against BA with fast vehicles, I can reliably get 2 turns worth of night-fight without any issue. Don't forget that the rhino need to get there to shine their searchlight, and once they get there, there's still a chance of falling short and even then, each of them can only light up a single target.
Searchlight most definately does not make NF a non-issue if the Necron player knows how to kite, god forbid you're playing DoW or even pitched battle, there are plenty of things you can do to ensure that no searchlight is within range until turn 3 at very earliest.
As for Gloom Prism, short of reinforced aegis, it's identical to Rune Staff. 4+ to cancel a is an odd i'm more than happy to deal with. As for them being slow, no slower than other MCs that doesn't fly.
Insofar as getting beserkers and DPs both into a fight with Wraiths, achievable with Lash I suppose but then you won't be lashing anything else, and the Wraiths should either be deep-struck or held back for counter-assault purposes. If you're absolutely determined to lash the wraiths, the rest of the army should make short work of those DPs.
At the end of the day, it all comes down to movement. Against Lash princes, battles are won and lost at single dicerolls. A 4+ gloom prism cancellation, a bad 2D6 lash roll or a bad spot distance roll means the Necron player immediately gets the upper hand.