Hi @geoviews!
Yes, safe to delete the old app, and also the files in the “Arc App” folder.
Your read is correct: the new app puts its backups and exports in “Arc Timeline” folder on iCloud Drive, and the old app used the “Arc App” folder. And the old app’s stuff isn’t needed anymore.
Personally I’d be still nervous about the delete, simply because deleting things makes me nervous 
But the new app doesn’t ever look in there, and has no need for anything in there.