I’ve worked under both systems, but isn’t the purity you’re describing a bit of a dodge in that you wind up force pushing amended commits when you find you forgot something?
Why is that a dodge? that's the expected way to work in this system, and it should be able to show you the interdiff between those amends.
Not once they hit master, no. You push bug fix commits.
People say they care about the "story" behind the PR. But no one cares about that story if it's about forgetting to fix a test and a typo in a comment.
The extra commits are just noise that make you think the original commit is a source of truth in a blame when it has been amended 3 times more in the same PR, but the link isn't apparent anymore.
Force pushing is bad to a published branch, not a feature branch (not that you really have force pushes in Gerrit anyway). There are versions of Gerrit tooling where you can have a branch as dirty as you want locally, but only the final aggregated change is visible for review of that's what you prefer too.