It's a nice theory to repeat, but it's not supported by history as you claim. Do you see evidence of the high end of the smartphone market disappearing? Any other major tech market?
Seems to me that the high end continues to be redefined as commodity tech catches up to the high end.
CDs, tapes, CDs, Digital.
B&W, Color, Size, Quality, high def, 3D, smart, 4K.
VCR, DVD, Blu Ray.
Growth of the low end of the market does not necessarily come at the expense of the high end. There is certainly no evidence that it does in the smartphone market.
Price is a big factor in market share. For apple to compete they would need to lower the price. Companies like Huawei or Xiaomi are growing fast because they have high end spec phones at affordable prices. Prices from different parts of the world ranges from $800-$1200 for an iPhone. These up and coming asian company phones are selling at $200-400 with high end specs. Look at the prices of 4k TVs or Bluray, when they were first introduced they were expensive but now they are much cheaper.