It wasn't a combat situation, so I would assume it wasn't deployed with any escorts, she was on training operations before hand and things had I believe been prepared for.
I think a 3rd LHD is seen as excess as with out all the elements to go into it, its just a big empty ship. Looking at it from the perspective of 2005, a 3rd LHD would seem crazy, many questioned the 2 LHD's, and openly criticized it, the original plan was four smaller amphibious ships.
Of course now, 2 LHD's are looking a bit small, next year we will form an ARG with 2x LHD's and Choules chock full at which point we will probably recognize we need other things. MV-22's, some sort of additional connectors, self protection for the LHD's, plus what ever the army needs, LARCV replacements, beach stuff, armed helicopter of some sort.
Operating the existing LHD's with significant MV-22's and say some sort of LCAC might not be possible, as we modified the original JC1 LHD design to cram more army into it, I believe limiting some of its aviation and related capability.
In other words, if the ARG is a one off and never intend to use that capability fully, what we have now is fine. Choules might not even be replaced and could possibly be disposed.
If we want more then we need to work out how to do that and resource it. A 3rd LHD might be looked at in that context. Your can't just buy another LHD, you will also need to workout whats going into it, how sustainable all that is. The purchase price is actually quite small in that context. Bringing it into service with the RAN is the easy part.