> Isn't Obtainium just worse than F-Droid?
No, since it avoids added another trusted party which has proven to be highly untrustworthy.
> antivirus scanning
It's performative.
> F-Droid still does better checks than something like Play Store, right?
F-Droid doesn't have a target API level standard or other basic standards that the Play Store and Accrescent enforce. They don't do any serious review, it's the same largely imaginary system as the Play Store in that regard.