I do the only comperition they have are the necrons as the best race in the game.

I guess you meant to say competition, but if you are saying that they (The Necrons) are tough to take down when playing as the eldar, then you must be pretty new to the game.
Necrons have a very slow build & recruit time, they only rely on the power resource (Killing their resource is simple), and beyond their basic infantry (which costs nothing) are units that cost a lot of money.

Personally if you play your cards right, you can overwhelm the necrons with any race, cause the necrons are the only ones that takes the absolute longest just to make a heavily fortified base as well as a powerful army.

And yes, Eldar does kick ass, but they are only as good as the player that uses them. For instance, If you played as the Eldar against the Imperial Guard but being used by an experienced player. You may know how to use the Eldar pretty well but you could get easily taken down by a player that knows how to totally utilize the Imperial Guard.
Sure, their basic infantry at first really sucks, but with enough time that player can amass a huge army and then in minutes you'd be crushed by the continous onslaught of guardsmen & tanks.
If you can handle 7 hard computers against you with no allies, then you can say that they REALLY kick ass.
Have fun.

Gyrannon