Few comments on the questions asked.
Consumer judge the Screen size by its diagonal length. i.e The number 5.8" Screen automatically means it is larger then the 5.5". Most consumer dont know much about aspect ratio. Hence at first many expect it to be iPhone Plus Screen area when in reality it is not.
iOS 11 and Apps update for iPhone X, is by Apple standard appalling. That is especially true in China, when information wasn't already enough in US, you could expect even less so in Chinese. I dont think Apple has ever had such transformation of resolution, screen area, aspect ratio, curved corners etc. Everything before such as the iPhone 5 and plus are all relatively simple.
More Advertising - That is true. But one must remember, it is not selling as good as those Analyst expects. Apple internally may have ( and very likely so ) different expectations. The iPhone X was suppose to be another class above the normal iPhone. That is why from the start it is priced so. But the market expects iPhone X to literally take over iPhone 8's role.
So why aren't they doing more advertising? Well, it wouldn't be a great time to do so when you have batterygate problem, which i would argue is 10x worst then Antennagate. Adding the constant bad press Apple has had with security and bugs.
And I will add my own take here on shipment numbers, which I wrote on a few forum and I have been verbally abused and seen personal attacks on it. Stay Clam and take it with a big grain of salt.
I think iPhone X in US and EU are doing ok. That is not to say demand are in expectation of Apple. I think rather it is weaker, but Apple is likely pushing every channel they have to reach their quarter target. What that means is it used to be consumers were queueing and scrambling to get a new iPhone, now Carrier actually have to push people to sign up and meet those target.
In China, Japan, South Korea, or pretty much SEA ( South East Asia ) region, I have never seen iPhone price reduction, promotion and other similar event happens within 2 - 3 months of launch. This is also the same to iPhone 8. This doesn't mean it is not selling well, it simply indicate the carriers and channel have committed a volume they now have troubles getting them away fast enough.
We will know soon in two weeks time when Apple does it quarterly report. If they miss their guidance, they could blame it on Batterygate. If they dont, the focus should be on next quarters guidance, since Apple could easily push all the stocks into arrier side and make it fit this quarters, but they will have to face the reality later.
Another point worth noting, which I dare any analyst to put it in their report, Within China there is a trend of using a Chinese Smartphone Brand within the political and business circle. Which is something President Xi wants. Although I have no idea how much of that has an impact. Since Apple is first and foremost a consumer brand.
On Dual Sim. I think Apple has an idea how it would implement Dual Sim, and not just in China but World wide, is that Apple would have both eSim and Nano Sim. This way Apple gets to push eSim in Mobile adoption and someday get rid of Physical Sim, it also means it could test Dual Sim settings. I hardly doubt Apple would allow you to put a extra NanoSim in since they think 3.5mm is a waste of space.
But Apple is having lots of trouble getting eSim to work in China. Not so much technical, but regulation. The sim and Phone number has to be registered to a real name, and my guess is that this put eSim at certain disadvantage. Such as privacy etc....... Apple Watch LTE, which advertise to work with China Unicom, never got pass the regulation hurdle. And Apple has offer full refund to those who brought it.