I am using an iphone 5s, 64 gb version - it's been my daily phone for since it was released. I've had no issues, other than finally replacing the battery this last year for $30.
Admittedly, I'm upgrading this cycle, but I'm super impressed by how long this phone has lasted. I bought a Nexus 4 (9 months older phone), and it's been complete shit for the past 1.5 years.
That's great - but the Mi5 came out in February 2016. I'm not sure why you can compare it to a phone that was release in October 2013. I would hope that the Mi5 would be better than the 5s!
I am not stretching it. I run the current iOS version on a 4s purchased in 2011. Battery is still working pretty good too. Not as good as when it was new, but the whole thing still works as my only phone without much issue.
You're right, I'm runnin 9.3.5, just checked. I thought I was running 10. Regardless, the 4S has been a true workhorse and I don't think Apple makes them this robust any more (obviously, Apple lost money on me by making such a reliable phone that I didn't need to replace it!).
You might be stretching it a bit there, but otherwise this point stands.