Huh. It's nice that he let the Knight be tied up, but it's perfectly capable of walking out of CC and shooting/charging anyway.
Anyway... The vast majority of Necron big guns is on a correspondingly big platform. Troops can't really make a good dent in vehicles, sadly, unlike in 7th where their Gauss guns worked wonders on tanks. While basic Gauss weaponry will still shave some wounds of tanks at a similar rate (usually wound on 5+ now, but then saves come in...), all tanks have 3-4 times more wounds than they used to have Hull Points, so that's a problem.
At least the Necrons have a ton of the very, very efficient Strength 5 in their weaponry.
Back on this list... I can see getting rid of the Doom Scythe, but it'll make your stalker the obvious target for any heavy long-range gun. Any vehicle with Quantum Shielding can take a beating and a half, but that might be a bit too much love. A second Stalker like
is running might mitigate that (and if you picked up more than one Start Collecting, you'll have one ready).
Other than that... Maybe embrace the "tie things up" strategy? Fit in more Scarabs, as the little buggers are cheap (plus, given the number of Warriors you have, you should have a few bases more of them), and good at tying annoying (non-superheavy) vehicles up and forcing a good amount of saves in the process. Should let you focus fire on one or two, and get there by sheer weight of fire?
TBH, given the uncertainty of what the Codex will change, adapting a ton right now might be the wrong move anyway. Wait for codex and paint might well be your best option.