Necron ships are known to have void shields in canon, I'm confused as to why they don't have them in the game. They're too vulnerable to being boarded as is without everyone and their mother lightning striking them. Plus their regeneration is too slow to even warrant not having void shields, and their higher than average ship costs and comparatively small number of attacks along with abysmally slow speeds and firerates mean they get overwhelmed too easily by factions that can field many more units, such as the Orks or the Tyranids.
I just think it's a bit strange that Necrons don't get them but Tyranids do (unless it's supposed to be some spore cloud nonsense rather than actual void shields). I mean, I don't think Necrons are vastly underpowered, but it does feel a little bit out of place for one of the most technologically advanced races in the galaxy to forgo shielding entirely. I'd be okay with reducing hull points on their ships just to have some form of shield.