A siege ship by definition is not supposed to be maneuverable, nor a PvP ship. She is designed to place massive firepower on a fixed position - thus the change from flight mode to siege mode. Think of an STF gateway, a perfect target for this ship. Or have one or more placed such as to cover the exit point of a wormhole. Probe duty is another place they shine.

She is a niche ship, and best used for the purpose she was designed for.