Arnor- Designed For Failure?

[tom the eldest]

But arthedain and cardolan wereable to hold the witch king for hundreds of years,with cardolan and arthedain working together,they could prevent angmar from invading.they cant directly assault cardolan because arthedain can sent armies from weather hills and struck their flank and rear.angmar was forced to make all-out assault,with several armies to distract the defenses while the main one going to cardolan.this show that if angmar dont use such tactics,then earnil(ur?)couldarrive in time.