To give you an idea of how divergent it has become, try:
This is the benchmark most representative of Discourse performance, and the absolute best known Android score for this benchmark is right at ~400ms on a Samsung Galaxy S6. That doesn't seem too bad until you compare..
- iPhone 5 → 340ms
- iPhone 5s → 175ms
- iPhone 6 → 140ms
- iPad Air 2 → 120ms
- iPhone 6s → 60-70ms
In a nutshell, the fastest known Android device available today -- and there are millions of Android devices much slower than that out there -- performs 5× slower than a new iPhone 6s, and a little worse than a 2012 era iPhone 5 in Ember. How depressing.
It's also partly because single core performance on Android is falling way, way behind iOS. Notice that the flagship Android device barely has the single core grunt of an old iPad Mini based on the old A7 core. Compare single core Android GeekBench versus single core iOS GeekBench:
I am no longer optimistic this will change in the next two years, and there are untold millions of slow Android devices out there, so we need to start considering alternatives for the Discourse project.
We did make significant changes to the Discourse project to work around this issue. See Robin's blog post for details.