Well, thanks for affirming that 95% of all necrons are mindless automatons. So, not really possible to make them as a player species...
Well that, and there's some big customization issues. Take the Necron Warrior, for weapon choices you can equip him with a Gauss Flayer or a Gauss Flayer, or if you really want to change it up then you can swap it out with a Gauss Flayer. Most everything beneath a Necron Lord has about the same level of customizability.
Necron Warriors may be the mass troop of the Necrons, but they are not the Elite. And the promise of the Game is be an ELITE Soldier. Necron Immortals, where befor the transfer in their Metal Bodies, Soldiers. Thus they did get better weapons and better Armor. And even then, there are many Necrons. Well if we leave Necron Warriors aside, because they are basically Zombies with Gauss weapons. And look at Immortals, they have 2 Weapon Choices. Not much, but you do have a choice. But do you need many option when your basic option is good against everything? Flesh? No problem Armor? No Problem Heavy Armor? Takes some time. And do not forget that there are other Classes also than would be playable.
I definitely would rather see the tau as a playable race and the necrons as slow moving npcs. The tau have way more options for versatility especially with the kroot/ havoc suits and castes. Necrons are too limited
They have enough Troops to fill the space for Assault, Tactical and Support Role. Their Vehicles are one of the thoughest in Warhammer. They are limited in Weapon variety, thats because their weapons are good in many situations. High Damage, High Penetration, slow firerate.
Reading this thread, I am overwhelmed by a strong sense of Deja Vu.... Almost like... like I've read it before somewhere...