Having recently gone through the F-Droid release process, I learned that this is not necessarily the case anymore.
F-Droid implements the reproducible builds concept. They re-build the developer's app, compare the resulting binary sans signature block, and if it matches they distribute the developer-signed binary instead of their re-built binary.
This is opt-in for developers so not all apps do it this way. I'd sure like to know how common this is, I wonder if there are any statistics.
The process adds a significant delay for updates but it does not actually protect users from developers in any meaningful way. This real world example with WireGuard demonstrates that.