Coldfire ballistas are absolutely terrific, and they are quickly becoming the number one tool against enemy zergs. This siege is extremely efficient, but it requires a certain amount of coordination to make the most of it. One coldfire ballista cannot do much really, but when combined with other siege, they can be simply devastating.
Yesterday morning, two AD players managed to literally bomb circa 20 unsuspecting DC players who were very tightly stacked on a resource flag near Castle Black Boot. Today, some 15 DC were instantly defeated when Black Boot's main gate opened and they rushed in without giving it much thought. Several well-timed shots from coldfire ballistas can definitely turn the tide in the defenders' favor, but a large amount of teamwork between the defenders is also necessary, as they must use other siege like oils, meatbags, and oil catapults. These two examples did not bring the entire zerg down (around 40 players today), but it might well happen at some point, as more players get their coldfire and defense strategies improve.
I totally adore how this powerful siege is rare and relatively difficult to get. Vengeance dolmens are a bit more challenging, especially solo. The drop rate is far from generous; it is only possible to carry one coldfire ballista at any time, and they are not infinite. It could be interesting to have access to Vengeance lancers, maybe obtainable from treasure chests very rarely, and limited to one, just like the coldfire siege.
You could always try actually fighting and engaging in PvP activities.