Has another codex hurt the Tyranid cause? Let's see.
Tyranid Advantages -
They're an army which likes to get close and nom you - Necrons are a short-ranged army with little nomming ability of their own. Super-gants, Genestealers, the array of MCs, Warriors/Shrikes, Ravengers, Hormgaunts, etc. are all going to do a number on your basic Necron. Even the tougher Necron units like Immortals or Lychguard are going to be wounded pretty regularly with lots of high-strength and/or poison attacks in combat. Once Tyranids get into combat the advantage is obviously theirs and they have some speedy units and the durability to get there against an army without lots of high strength/low AP weaponry.
This lack not only helps the standard T6/3+ monstrous creatures but the T4/W3 medium sized critters - there is a lot less S8 firepower being thrown out from the Necron side of the board which allows these units to be more effective. Same as in combat - no more Power Fists causing six wounds by themselves - S7 with a smattering of higher strength weapons and Entropic Strike is the name of the game for Necrons.
The lack of true tanks for Necrons overcomes the Tyranid weakness to being moved around by the opponent - although they may still suffer at taking down opponent's mech they aren't going to be taking the double whammy of not being able to kill them all and being pushed around the tabletop willy nilly. Monoliths can still do this but are slow and have lost their immunity to scrabbling MCs in combat. This gives Tyranids, particularly being an aggressive, move-forward army, a lot of options in midfield in terms of objective controlling and tabletop control. Although they are still going to have a hard time dealing with mass AV, most of the Necron vehicles aren't fast so are only moving 6" if they want to shoot (and are limited by range). Scythe based armies obviously open this up but are much more susceptible to Tyranid firepower.
The firepower of Tyranids is also relatively important as anti-infantry. As usual it's not huge due to lack of options at range but being able to put lots of blasts and templates out alongside S6 firepower can stop the Scarabs from clogging midfield and chewing through your Termagant lines. The lack of serious ranged options on the other side of the board also ensures Tyranids will be firing back if they are being shot at - all the Tesla is 24" ranged which means Hive Guard aren't going to be crying about range issues unlike against other armies. Doomsday Arks can be annoying though...
Necron Advantages -
AV13. Tyranids have a hard time with 10+ AV11 vehicles and now you want them to deal with AV13? Even spammed Night Scythes are going to give them issues and because they are fast enough to stay on just the edge of Hive Guard range, Necrons can pull the shooting elements of the Tyranid army into positions more advantageous for them. AV13 on the other vehicles is just a kick in the nuts and Night Fight can help reduce the early game effectiveness of Tyrannofexes to get those early destroyed results. Living Metal also shoves a spanner in the works for Tyranids - their ability to cause decent suppression and reliance on such is far less effective against Necrons as they shrug off most of these results.
Entropic Strike is also a serious factor against Tyranids and their multiple wound creatures - one hit and failed save from Entropic Strike and your save is gone for the rest of the game. That durability against the lack of high strength/low AP weapons goes out the window without cover or FNP though in combat this should be less of an issue against the lower strength units of Necrons (i.e. wounding on 6s). The dilema here for Necrons is applying Entropic strike to the Tyranid MCs - something which will be denied as much as possible with bubble-wrap and smaller units. Harps are pretty much their best option here but aren't exactly reliable needing a 3+ to hit, 4+ to wound and then a failed 3+ save but if that does go through...
Other Crypteks such as Tremorteks can hurt Tyranids as well. Although most Tyranids have move through cover, forcing lead or key units to continually roll difficult terrain will take some movement away from them - whether it's simply an inch a turn or maxing their move at 2" - it keeps the Tyranid army at bay for that little bit longer which allows the Necron firepower more time to impact the game.
Ironically some of the lesser seen units of Necrons can give Tyranids hell if everything works out for them - Warscythe Lychguard or Necron Lords will ruin any MC's day that is not a Hive Tyrant or Trygon - it's one of the few places I2 comes in handy. Outside of this though such units aren't going to be scaring the usual Tyranid gribblies in combat. That being said, Necrons do have some combat options to deal with Tyranids. Wraiths don't have some of the issues they do against other armies where mass S8 can simply lol them off the board - Tyranids have that only from their anti-tank which is stretched thin as is. They're not super great against MCs but can put out a nice amount of rending hits and tie MCs up with their 3++ and aren't being insta-gibbed without Boneswords. Scarabs are decent and not so decent - Tyranids have a lot of blasts/templates to do lots of wounds and S6 firepower in both shooting and combat but Scarabs can make a reasonable meal out of the bubble-wrap Tyranids use to protect their important targets or tie units up for a fair amount of time.
There's a lot of give and take here. Mass AV13 can really hurt Tyranids but due to their generally short-ranges, they don't care so much about Night-Fight outside of Tyrannofexes - they want to be closer to their opponent. Inability to reliably drop mass AV13 can hurt though and even when AV11 comes into play, mass quantities of it can still give Tyranids a fit. Tesla is going to be a pain for the usual layered Tyranid approach as well - it gets free hits on all the bunched up units and is relatively decent at putting wounds on MCs due to strength 7 (no one cares about the AP - here). At the same time, it's all about wound torrenting to drop those MCs outside of Lanceteks and with 40+ T6 wounds running at you and some FNP, there's a lot of pressure for those Lanceteks to be working. Even 10 of them is only going to cause 2-3 wounds a turn. Beyond this, Necrons have quite good anti-infantry firepower with Gauss and Tesla but it is relatively short-ranged, particularly Gauss. If this is firing at full effect then the Tyranids are likely in your grill quite quickly.
That being said, outside of a few units, once the Tyranids start breaking into the Necron forces and can stay there, the Necron advantages become drastically reduced. Entropic strike can still pull a number of Tyranid MCs but they are pretty much ripping through whatever they touch and are generally wounded on 6's. Pretty much every unit in the Tyranid army, particularly when backed by Hive Tyrant/Tervigon buffs is going to chomp on the robotic Necrons and without the plethora of high strength/low AP weaponry other armies boast, the durability of the T6 and T4/multi-wound models of Tyranids are more likely to reach there intact.
Overall it's a pretty close match-up. Tyranids struggle against the armor of Necrons more so than usual thanks to AV13 and Living Metal when massed like they do against most armies but they're not being moved around the board by such nor being shot from 48" across the table. Their durability isn't actually circumvented by the firepower of Necrons but Necrons can still put out a lot of wounds on tough and bunched targets, have entropic strike to weaken MCs and very effective anti-infantry capacity. Ultimately, if the Tyranids can make it into combat and stay in combat rather than being shot after each phase, they're in a good place but Necrons will often have more board control thanks to their durable and hard to suppress vehicles. If they are able to block/blunt incoming assaults with efficient movement and use their firepower + entropic strike to good effect, they can do a number of the Tyranid army.
So once again we get a match-up where the army is able to apply their playstyle and strengths more readily than their opponent is more likely to come out on top - always a good sign and indicative of a more balanced match-up (and not one which sends Tyranids crying back to their maker).