Why might an arb be more effective in stabilizing blood pressure than an ace inhibitor?

ARB vs. ACE: Different people respond to blood pressure medications differently -- so in some people, an arb may be more potent than an ace, and in others vice versa. These medications work at different parts of the renin-angiotensin pathway.

Usually it's not: For most patients there is no advantage. A few patients have a severe cough taking an ace inhibitor, which does not occur with an arb. A very few patients can "bypass" the ace inhibitor with other enzymes that convert angiotensin, and these will benefit more from the arb. However this is unusual.