Why is Moridin considered so inept? Is because he was beaten 3 times and once killed by Rand? He is a servant to the Lord of the Grave is he not? Considering that and his personal philosophies, I'm sure that death was not considered a complete failure, he has succeeded in alot as well. It is pretty obvious that a direct approach won't defeat Rand, and yet that seems to be the tactic that Demandred is most suited for. Consider also that he hated Lews Therin because he was second best, lesser in every meaningful way.

Demandred surely plays an important part, but don't judge him the Shadow's best weapon before you've even seen his successes or failures.