Removing many of those assets via brute force doesn’t seem very practical, because I assume the editor will become unusable, unless I keep a 2nd copy of the editor around and build solely through command line. These are assets that are never, ever, referenced in shipping builds for any platform: editor visualization materials, editor tutorials, editor debug assets. There’s 24MBs worth of engine debug materials, for example. Even the material used by the editor gizmo and the grid are there.
Also, my attempt at disable specific startup packages failed. It seems platform-specific config files are only used during runtime, not packaging, so I would need to disable those packages at the editor-level, which again would break the editor.