It is my understanding that a repair is much simpler for an iPhone purchased in one country than a full swap (or in your case AppleCare Express replacement). In my old store, more than once, we would have to replace a phone that we were unable to repair. If the phone was purchased outside of North America, the best we could offer was that a replacement could possibly be available in 2-3 weeks. This did not go over well with most customers who were traveling…
Not all iPhones are the same across the world. Some countries require slightly different hardware to prevent access to some features. Most of the time it is software related.
Express Service seems to be limited to country of purchase, however one should be able to visit an Apple Retail Store or AASP for a full swap under Apple Care. I’m sorry you are dealing with this. If you choose the Alternative Solution, feel free to swing by the US and pick me up 