There's a nice video about this from Louis Rossmann [1] that talks about this in detail and tries to find some reasons for it, and he seems to suggest that the update was never about improving the battery life as in getting more usage per charge out of the battery, but improving it as in limiting the battery full charge capacity to minimize potential problems with it, because he (and others) assume that they identified bad batches and are trying to fix potential problems with them by limiting it.

[1] https://www.youtube.com/watch?v=Xboo6sV-cJU