Consider this (and with all due respect to the often-right Ming-Chi Kuo): any time any company sees a downturn in a cash cow, primary product's sales, what do they do? Unless they lack funds (no problem here), they significantly amp up the marketing to try to drive more sales. Has anyone noticed above-average iPhone X marketing volume, such as more commercials than normal, more print than normal, more electronic than normal? I have not.
If iPhone X (and presumably 8) are suffering from disappointing revenues, does Apple just accept lower demand and do nothing about it? Why would they? The first thing they could do is crank up Apple marketing. The second thing they could do is appear to cut the price in creative ways- such as through third party channels via financing offers, making offers of the new X at as little as $0 out of pocket (just sign here). Are we seeing much of the latter? I'm not.
Now, this particular article seems to imply this "problem" is in China. So maybe the American market is about normal but things in China are less than expected. If so, Apple would be cranking up the marketing and reducing the barriers through creative financing offers there. Are they?
Can someone(s) there chime in and confirm or refute that you are seeing much more than average Apple advertising efforts in China?
Next, Apple has seemed to shift focus more and more to that market in the last few years. I even suspect the 8 exists because 8 is
an especially magical number in Chinese superstition. As such, I doubt there will be an iPhone 9. But bigger picture, if the Chinese really want (almost only) bigger screens than these, I suspect Apple's ever-growing interest there would have picked up on that and we'd already have an X+ for that (ever-more-important) market. X+ did not have to wait for the Fall of 2018 because Apple was already rolling out 3 phones in 2017.
Lastly, if sales of the primary, revenue-dominant product is down for this reason- that a big market wants the X+ now- why does the X+ wait until next fall to roll out? There's nothing structural that forces Apple to only roll out new products on what seems like an established schedule. And if revenues are trending downward for this reason, the easy fix is to build the X+ sooner than later and roll it out sooner than later. A company with Apple's resources doesn't just lay back and suffer the consequences of revenue downturns because they want to persist a schedule of only rolling out new tech in September.
Put all this together and I suspect Apple is about on pace to make their numbers. Internal panic would show in more tangible actions (marketing) if sales were way down. Apple is not going to announce a miserable quarter and weak forecast while sitting on a mountain of cash and appearing to have made no special efforts to do anything (more than normal) about it. Such inaction for no good reason would look like bad management.