The main point to make is that the expats don't actually work for the airline. They work for an agency who pay the market rate from the money the airline pay that agency to provide the pilots. The expats are on a contract with little security and can be out on the bum at a whim.
It's market forces which dictate pay and not the kindness of the airline. The local pilots signed the contract and got the going rate for their circumstances. If the Chinese guys want pay equality, they should leave and apply to an agency!
(PS - before someone points out they can't - I do know that!)