It feels similarly wonky for dps and I agree completely.
I assume you can make some kind of "if no target, target last target" macro combined with the finisher you want but I haven't had the.. energy, to get it done myself.
It works like it did in retail at its worst, which I assume is wotlk since that's the ascension patch, but in vanilla for example I don't think the target was cleared after dying so combo points weren't so easily wasted.
Devs could really improve on it.