Author here! I had searched around but didn't find any existing app that matched my requirements. A few that immediately come to mind:
1. I have sole ownership of the data
2. The data is stored in an easily parsable format (TSV)
3. Duplicating a recent activity takes one tap
4. Pie and area charts are displayed in the app
My app is open source and available on GitHub[1] for any Android developer to compile for themselves, but if there's enough interest I can also get around to packaging it up for the Play Store/F-Droid/etc.