Ok, given what I know of your understanding of the damage formula, the notable distinction you make between damage cuts and defense buffs doesn't really make much sense to me.
If you're not setting up to stack damage cuts, then in practice, a +30% def buff basically is a 23% damage cut, except longer duration. That's not so significantly worse than the higher end damage cuts to the point that justifies 'damage cuts are useful, but defense buffs are garbage'. There isn't exactly a big gap between the two until you deliberately start stacking up damage cut/reflect/element tolerance.