While we are getting faster flagship phones every cycle, the vast majority of people can’t afford these. The more affordable phones are stuck in the past and have highly fluctuating performance metrics. These low-end phones will mostly likely be used by the massive number of people coming online in the next couple of years. The gap between the fastest and the slowest phone is getting wider, and the median is going down.
Das makes some excellent points about writing code that works fast on all devices.