Xiaomi do copy Apple, but they do it so much better than Samsung. Xiaomi actually have taste, which is why, in my view, in the longer term they are a bigger threat to Apple than Samsung has ever been.
However for now they are a bigger threat to Samsung, because they are grabbing that middle market. Indeed it is primarily because of Xiaomi that Samsung are losing ground, with margins being squeezed. Samsung are now in a vice between Xiaomi and Apple.