I dunno how bad it is, I enjoyed it.
Why is the file 400MBs though, did you copy paste the models and textures and other various resources into .tscn scenes - instead of saving out the resource into their respective binary file formats? …no, it turns out the addon Proto-CSGs includes something like 50x 4MB png textures of colored grids - you can fix this by excluding certain folders from your exports in the export UI.
Likely the download would be under 150MB after doing that.