While I haven't tried it on base structures the damage on units seems to be comprable to other rocket arty. the spread on the rockets seems decent and take a while for the rockets to come in meaning you will lose models but have a chance to react (unlike with calliop). They need to have decent arty as they honestly have none other than this commander. Trucks shouldn't mean you are invincible to arty and have received numerous buffs to stop people from satchel charging them/AT gunning them into oblivion.
I will see if the rocket ary is any different but you should be testing them at max range and close range as the scatter will be way different.
At half price