pm713 wrote:They're both ancient, have incredible tech, lost their great empires and seek to reclaim them, have issues with younger races.
I feel like you missed my point. Saying Newcrons and Eldar are the same is wrong but it's the same thing as saying Tyranids and oldcrons are the same.
That is where you are already going wrong. The Eldar for the most part don't seek to reclaim their ancient empire. They realise they are a dying, dwindling people, tired from the long ages of decline they have endured and knowing that is likely that they will soon disappear. Elves in space basically, that is their theme. Necrons on the other hand have slept for milennia and are now on the rise again. That is not similar, that is in fact a completely opposite narrative theme.