If we're talking about running through things quickly, I use Doom Spike on 3+ targets all the time. As EasyModeX said, it is not TP efficient, but I've yet to come across a time where TP efficiency is a bigger goal than burning down groups fast. The only time I usually ever need to use Invigorate is when I Doom Spike spam.
I suppose a good middle ground is: if you have Invigorate up, spam Doom Spike. If you do not, then use HT + RoT.