I have a very similar Southron threat deck. My initial reactions are as follows:
-Having too many Red Wraths doesn't do you any good because they're hard to play, especially as you're using
Southron Spear which conflicts with
Red Wrath. I would lose some of either so you're not pushed for vitality, probably the Southron Spears because
Red Wrath is a surprise and therefore much more deadly.
-Mumak is not that good; you need to replace both of them with
Mumakil, which are MUCH better for a threat deck.
-Mumakil of the Harad I've never found to be all that useful - another
Raider Bow or
War Towers will ultimately be much better for you (and you definitely need a fourth
Raider Bow!)
-Fierce In
Despair is good and fun, but I suggest you conserve your twilight on what's
really important: killing companions to trigger the threats! Perhaps another
Southron Bandit or two would be more worth it.
Thranduil