Yah.. I also think avatar of melandru is currently problematic. One would think they'd at least make it so that you use some energy then maybe lose some upon successful casting of the spell.
I'm not a fan of avatar forms though, the down time on them significantly hampers a dervish's effectiveness in the battle field, especially after the increased energy cost on most of them.. I don't think they're worth it..
As for the other elites, I don't think they're where the dervish's potentials are. Those elites are put in there to help you manage your skill bar more easily. We already know that dervishes cannot spike nor shutdown, so they have to rely on pressure damage to kill people. Deep wound, bleed, cripple, etc are pretty much a must if you are going to use your scythe. However, if you go mysticism + wind prayer + scythe mastery, you'll find that there're limited ways for you to cause bleeding or deep wound. Wounding strike comes in handy then, as it filled in the blanks. On the other hand, if you have aura of thorns from earth prayers on your bar, you would take reaper's sweep since bleeding is already covered, you take reapers for the added damage.
This is different from say necros, who usually take an elite then form a build around it, dervishes first form the build, then take the elite to compliment.