I agree with you on sailing cats, but big powercats have no lack of space as I understand it. The 50 m as above will have a beam of about 17 m / 55´.
The inside space on the main deck will be 400 sqm and the deck above 260 sqm and the upper deck 144 sqm. The hulls will have liveable space of 80 sqm each (plus engine rooms) totalling 960 sqm indoor living space! (I guess you add a zero to have it as approximate squarefeet?)
Add to this the extensive deck areas and I think a big power-cat is more than justified when it comes to available space. But you will have to pay extra for the beam in many ports...