If foes combined OB/DB is half of PC's, the fight will be dominated by the PC's.
If combined OB/DB id 3/4, foes will land an occassional blow.
If combined OB/DB is 1/1 ratio, without terreign, tactical or magic advantage, it is anyones fight. Obviously, who ever gains one or more of those advantages will most likely carry the field.
The advantages of ignore bleeding, ignore stun, crit reduction and LA/SL is the monster needs less DB (they are harder to hurt) and less OB (they don't parry much).
Ignore Bleeding: the weakest of the special defensive abilities (primarily because most GM's do not track penalties do to blood loss), this ability will keep foes up a bit longer. Consider it to effectively increase OB/DB by 10.
Ignore Stun: A very powerful ability. Consider OB/DB increase to be 40. If foe is LA, then 55. If SL, then 70.
Crit I: effectively a +15 OB/DB increase.
Crit II: effectively a +25 OB/DB increase.
Crit I and II#: consider a +55/+65 OB/DB increase.
These are just guidelines and not rocket science and may only express my opinion.