Most of the Webway pathways to Commoraugh are not Shipways. Battleships and Battle Barges would most likely not be available to bombard it if the Legion only managed to breach normal webways, which are tank sized if not smaller. If a Legion breached a shipway, it would be difficult to hold off the Imperial Fleet, but even so, the DE have quite a significant fleet presence themselves.So the dark eldars have the home field advantages . I imagine there be heavy damage on both sides but I think the legions have the advantage with the battle barges and battle ships. I mean if there was a path way to Commoragh why not just bomb the place like crazy and get out the same pathway?