I agree with the first part of that statement, but the B787-9 fitted with an international configuration won't have have the pax numbers to replace the B744 without the cost of increasing the frequency.
Looking at it another way though, customers tend to prefer frequency over capacity, especially those that wear the suits and sit up the pointy end. It could be argued that the uplift in yield, coupled with the lower unit costs of the 787 may actually see more in the company's coffers than keeping to the status quo.
In an ideal world, QF would use their 787s to open up new routes. Problem is, I'm not sure that QF knows how to grow a route anymore. Maybe a new 49% shareholder in QF Int'l could mix things up a bit?