As they have been less than helpfull
You are underqualified. At present CX new hire S/O's (second officers) are at anywhere from 3500 - 6000 hours, many with real experience as F/O's on medium jets, some even as Captains on A320's and B737'3.
If I decided to join Dragonair would I be able to upgrade to Capt
I don't work for Dragonair, but I do know quite a few of their F/O's who are vastly more experienced than you, been with them for many years and are still awaiting upgrades.
I would imagine with command time on the Airbus it would make me more attractive to Cathay.
I don't know if you're familiar with the ratings that you can buy privately, but it gives you only a rating, no command time. For it to be meaningful, get some real hours on type. CX does not look favourable on PFT jockeys. But, if you really have $20K to blow on a piece of paper that will do you no good at all, go right ahead.
My .05c - get out there, get some multi, complex turbine or turboprop time and then the (aviation) world would be your oyster.