I find rock lobbers to be great when fielded in pairs, giving Orcs some range that they usually lack. 150pts to, on average, destroy one stand of enemy heavy armour at a range of 60cm is worth it for me.
I like this way of thinking
the choice may be sub-optimal, but it's still useful
in the context of the listI do find the warmaster lists a bit strange in that units appear to be costed in isolation and don't take in-list synergy into account.... if someone developed stats for the chaos hellcannon, should it be costed in line with artillery-heavy armies like dwarfs or empire, or should it be costed with the fact that it's sitting in an army with the toughest infantry and toughest knights in the game, and being able to soften up targets at range makes those units even more potent...
the high elf dragon is specifically overcosted so its inclusion is a theme rather than skew choice, it can be effective but it's sub-optimal, I view the rock lobber in the same light