It's offensive power is plenty good, it's just a little too easy to kill imo. I know most other rocket arty dies in 1 shot but at least they can reposition quickly. Calliope can take damage and reposition quickly
Unless you see a nebelwerfer. LM is the only TW rocket arty available. Thats why its not as mobile as, for example a pwerfer.
You just cant have a heavy rocket launch platform rushing faster than a bfc (big f*** canon) ATG, its not appealing nor realistic.
Calliope is not a good example to compare with, unless you want a cheesy buff, of course.