Apple has had roughly double the hardware speed of anyone else since Fall 2013 when the A7 chip came out. They stole a tremendous advantage there. So even their 1.5 year old phones are roughly the same speed as newest Android phones (e.g., iPhone 6 vs Galaxy S7). Apple phones that have the same performance have actually been cheaper than their Google analogs. So people have been buying Android phones for emotional reasons or in order to avoid owning Apple products, which have an image of being mainstream rather than 1337.
However, by next generation we can expect the 64 bit lead they stole to have been closed. Qualcomm will get there. Therefore, we can expect people to be able to purchase Google phones on rational bases again.
Once that happens, only a minority of people will buy Apple anymore. The party Apple's been enjoying will be over. Almost all phones are nearly indistinguishable from Apple phones now as well. Down to every little detail such as the shape of holes used for speakers etc. So Apple's design advantage will also have been neutralized.
If someone like Samsung can come up with something new that iPhones don't have then there won't be any contest.