> by the time batteries wear out, most people are going to want a new a phone.

Not true. In recent years smartphones do not advance much, and would be perfectly fine to keep working if not for the dying battery.

> At the very least we'd need to see some data that shows that most people replace batteries when it is possible to do so.

The degree of "possible" varies greatly depending on the available expertise and spare parts. Right now in EU it's cost prohibitive for both coz the special labor required is expensive and almost no official spare parts for consumers. So of coz this will be no data to support your claim.