I can't help thinking that's what the enrage really should be like.
Also a real enrage is usually a big indication that you're out of time. That means increasing damage over time to the point where your healers cannot possibly keep up. ADS just keeps doing the same damage, and I believe most healers will actually be able to keep going for a ridiculously long time mana-wise, at least long enough to kill ADS several times over.
T2's "enrage" really does seem to be an oversight as it's actually easier to heal than doing it the normal way.