Going by ICS stats (and OP does say we're using legendary stats) - derived from volume, the Lucrehulk has greater shield dispersal than the ISD has output; the ISD couldn't bring its shield down by bombardment. IE in a gun battle, the ISD can keep firing until its fuel runs out, and can't hurt the Lucrehulk.
In the various cutaway shots, the Lucrehulk has
three generators bigger than the one on the ISD, one in the core ship, two main generators in the ring (that Anakin shot).
FTeik wrote:A game-changer could probably be the Skipray-blastboats and Assault gunboats the ISD carries aboard, since the Lucrehulc has nothing comparable aboard. Also the human crew of the ISD might be capable of outsmarting the rather limited droid-brains of the TF-battleship (although imperial crews haven't shown themselves to be very smart, too, but that might be a bias of the source-material).
The top end of Confederate crews, like General Trench, known for having developed tactics that largely defeated the use of cloaking devices, aren't demonstrably worse than the better Imperials, and reasonably the average ability of a late war Lucrehulk of the type shown is probably similar to the Empire's; most of its officers will be combat veterans, while the younger members of the ISD's crew may well have careers mostly filled with police work and chasing smugglers.
As for gunboats, the Lucrehulk can always task some of its three thousand vulture droids to bring them down?