I feel like the "something new" was price. Over time, that price kept creeping up. Yes, it went from being a 95% flagship to being a 100% flagship, but it also went from being half price to full price.
It was also cool that it used Cyanogenmod which meant you got a community OS that actually got updates, but over time other manufacturers started offering updates for their phones (rather than abandoning them soon after manufacturing). And that was something new other than price. But I think the big thing was that it was a half-price phone when it launched. In 2014, it was just such an amazing deal. Today, it's the same price as Samsung phones.
That really sums it up to me, then OnePlus phones are pretty standard Android phones, they are not really special, at least not to the extend where the brand means all that much to all but a minority of people.
I paid 130 euros brand new for my Nord CE 5 with 8GB/128GB configuration. Couldn't be happier with the purchase. All I care is about price/performance ratio and the years of updates promised.
It's expected that in 4 years our debt to GDP ratio will reach that of Spain right now. And Spain's ratio is decreasing. We'll be right there with Greece, Italy and France soon enough, and I doubt unemployment will get any better.
Xiaomi appears to be the 3rd largest smartphone manufacturer in the world (behind Samsung and Apple). Not sure I'd call them a "minor player"