This looks like something that'd be really useful as cast on crit or some other stuff, but not really very good for a dedicated self-cast pure minion character, and that disappointments me, because the only way those types of characters are viable is with high level map uniques.
A whopping 17% off! Talk about savings, that's almost an entire fifth off the regular price!
How do you seriously have trouble avoiding the dominus groundslam? He gives you upwards of 5 seconds to get out of there.
I'm pretty sure it does more damage the closer you are to him, so as long as you actually move away even if you don't get fully out of the range you'll take significantly reduced damage for even attempting to avoid it.