At the beginning of the war, before the Abandoned Land was breached, Grandmaster Ancestor Taixuan did not summon Gongsun Cuo just because Biluo was weak.
He had already devised a plan, aiming for greater battle achievements, to defeat the alliance of all realms in one decisive blow, and completely crush their main armies in a single battle. Thus, he deliberately used weaker forces to resist the alliance, attracting all their attention here.
Once all the allied forces charged ahead and gathered together, he would activate the coordinates, allowing Gongsun Cuo to breach the Abandoned Land.
However, before that happened, not only must the armies of Biluo's various sects and the Fallen Angel Army, along with the armies of many subordinate worlds, stand firm, but these Creation Great Powers must also hold their ground.