As of October 2017, JS perf in Android / Chrome is substantially improved, probably 1.5x - 2x speedup.
As of June 2018, Qualcomm has semi-competitive (iPhone 6s territory) hardware with the Snapdragon 845. It looks like their new release coming in 2019, the Snapdragon 855, will be close to iPhone 7 performance.
We do have to wait for the vast bulk of old Android devices to cycle through the market, unfortunately. I expect that will take another 4 years.