In truth, it was actually more likely the Consortium wouldn't do anything. Defeating a Platinum-led Stronghold was doable, easy even. But to do it with such sharpness and quickness that the Ersatz wouldn't even have time to respond, was almost impossible.
The most dangerous part of sieging a Stronghold was the risk of retaliation. It was the fact that during the invasion, it was very much possible that the Ersatz would find out about their attack, and send out their forces to support their Stronghold.
And by that point, the Consortium would be the one on the defensive, trapped in a Pocket Dimension that wasn't their own.
Even with the most detailed plan, it was very much possible that an Ersatz soldier would slip through the ranks and get out. It would only take one. And by the time they exit the Pocket Dimension, the rest of their forces would immediately charge to retake their Stronghold.
So, for the Consortium, sieging a Stronghold was never the first option.
