Installation and Upgrade are distinct activities, so Pre-Upgrade is still the applicable term. The tool is used after installation, to assess the ZIP archive before executing the actual migration.
Note - I can’t recall if the dependency on a target-version installation has been removed (i.e., if the tool can function independently using a “database” that it ships with containing the necessary content, as opposed to comparing the ZIP archive against a target-version installation).
UPDATED - I suppose the steps in the latest version of the tool (link) answer my question above. However, I’d still like to know if there’s a standalone version to use for Upgrade assessments, versus executions.
As for the term legacy, I am with you - hence the " " surrounding it 
KM