Theo is 3/4 right. This is also coming from 2 orc players!!! The Grunt is a backbone warrior with 800 life. Even with 800 life, they can take on knights and aboms with caster support or with other units aiding them. Also, I have ended the game by the time I need Tauren. But there is one other unit that is effective and works well with Grunts.
TEH RAIDER!!!
Because of nets and the fact they destroy buildings just as effectively as demos. Plus with Pillage, you can add money to get taure later. However, you need to treat them as a cross between hh and grunts. Cause of thier medium armor, they won't survive melee combat too fast. They shouldnt be attacking ranged unless u want them to assist. However, they do more damage to casters and make it easier to pick off runners, trailers or units being microed back. Truly an amazing wolf rider, which is why he is in my avatar.
Difficult to fight as well when you have grunts. Actually, ANYTHING is difficult to fight with grunts around. This is why you can go air vs fiends. As long as you have enough grunts to keep the fiends occupied... you can use them. Since they have three options:
1) Get the wvyerns at the cost of fiends to grunts
2) Get the grunts and let the wyverns attack.
3) Get the hero so he runs out.
Raiders are harassing masters and good support units, just not really strong battle class warriors as the foot soldier grunts are.