This is a different situation to the CX case, you are not being offered a job in KA but with another company on far worse COS. It is intended that new FOs and DECs take promotion and advancement opportunities from KA pilots.
You will not be on the Dragonair seniority.
You will not be able to join the Pilots Association.
You will not happily fly for Dragonair in the future because that is not what you are joining.
You are not being asked to fight our battle, you are being asked to stay out of it.
There are many places where an IFALPA ban does matter and that could well affect your employment chances in the future.
Just make sure you know all the facts and consequences before you make your decision.