Rage is actually an AOE, the same as Rest. The augment makes it great, too, since it's based on incoming damage and not your outgoing weapon damage. Meaning it's multiplicative with all forms of outgoing bonus damage. Very powerful ability. The speed buff is... questionable, though. I'm not clear on the reasoning behind it. Unlike MP, it doesn't accelerate spawn rate because it only affects local enemies.
That being said, I completely agree with your sentiment. Equinox should not lose her buildup when switching forms. Being able to auto-dump Mend & Maim is nice, but not as useful as u