The problem, as far as I can see, is that Xiaomi has no USP. In fact, almost the entire industry is commoditised and USPless. If you want a laptop or desktop, the important part - the ‘differentiator’ - is nearly always the same (Windows). If you want a mobile phone the situation is the same - except substitute Android for Windows.
Apple has played a canny game, albeit one that nearly killed it, in retaining its USP. You can complain, and many do, that Apple’s products are overpriced - but what you can’t deny is that, where it counts, they’re different. And if you want the benefits that that difference confers, there’s only one choice (it’s up to you to decide whether those benefits are worth the money or not).
So, given that one Android phone is much the same as another (differing only in performance, from sluggish to not-the-quickest, and in build quality, from plasticky bin-fodder to best-in-the-business) and given that the market is saturated, with every niche from the cheapest to the most expensive filled, why should I choose a Xiaomi over a Samsung or a Xperia, a Huawei or a Pixel, an LG or an HTC?
I’m sure that the Xiaomi will be very acceptable - but acceptable enough to muscle in to the established encumbents? The Xiaomi boss might fancy himself the reincarnation of Steve Jobs (complete with unacknowledged children?), but it takes more than a silly outfit to claim that mantel. Xiaomi will need to own their stack from CPUs, through to OS, if they want a real USP - and they’ll have to innovate with it (innovate - not invent, necessarily!) - but I don’t think that they have the chops or imagination to do that.