For strat balance ballist need balance tweak against catapults or you have to rework siege eq HP because now I just can 2 shot large craptower with 2 shots of cataplt.
To be honest catapult is really laggy but in good hands can shot almost from every position (even close to really high wall) to almost every target on map.
But ballista can unbalanced or kill lots of siege EQ.
Fire ratio can make it able to destroy every frouard base eq chest even behind siege shield, guy with shield or catapult in no time with small chance to defend that.
Now if you will able to destroy balista with arrows IT may make some sens but it cant be to easy( nowdays catapuld gets destroy from arrows in no time).
Just be careful with that beauty.