Do you have any data that suggest that the reason Apple's sales are decreasing is because they are loosing markets to competitors, rather than simply because the whole market is not growing as much as it was previously?
Not sure if such data is public. That's my own deduction, based on apparent slowing down of innovation in Apple. It's natural to expect to fall behind competition in such case. If other manufacturers would start reducing production too, it would indicate, that market is now now not growing as much as before.