It is trivial for the Android ecosystem to replicate an Instagram for their platform, it will be much more difficult to do this for AR and thus will be a meaningful source of competitive advantage.
There are real economic barriers to having the necessary hardware for AR. High-end Android phones don't ship anywhere near the numbers of iPhones to give it the scale required to make the necessary investments in hardware and software worth it (both from OEMs and Google). And that will ultimately limit the opportunity and market for developers, disincentivizing them to invest in it.
This is an area where Apple's scale, margins and ability to deploy new technologies and see meaningful adoption from users and developers (think about how fast Touch ID rolled down into the entire iPhone/iPad installed base, setting it up for Apple Pay years later) pulls up the ladder on would-be competitors.