Sometimes, I can't believe people. Shadowrath with low health and no armour and only melee are probably one of the WORST direct combat units. Shadowrath will only work for assassination above 1500 unless you mass them, and even then, it only really works if it's a large surprise and you're on the defensive. If you have the other person on the defensive, they will have castle archers to help defend and those will rip through shadowrath due to a lack of armour. If you are on the defensive, the other person can easily scout you if they want. If they scout and see shadows garrisoned, they can expect a rush and will build walls to block you and albows to decimate the shadowrath.
I dare you to try shadow mass against anyone above the 1600s or even the 1500s. It rarely works. Spearton mass is probably better than shadow mass and that's saying something.