Assuming doofos build and the 5 t2 bonus the average HPS of regrowth r3 is about 390 not including hots ( and at 633 +heal). The average HPS of Ht r3 is about 415 so if you add hots it might well be just as good or better. The selling point is that the average cast time of regrowth r3 is 1.46 versus 1.91 for HT r3. So in a raid enviroment that lower average cast time will raise effective HPS of his build by quite a bit.
The big problem however is the mana inefficiency of his build is ridiculous and that makes it kinda hard too recommend. I find it hard too believe you could use regrowth on a long boss fight and not run into mana problems, not too mention the tank may take too much damage for regrowth too be effective. So for boss fights you lose 9 percent mana reduction. In my opinion if your having trouble on trash go for this build else the HT build is better.