You're really reaching here. In order to make an Edenic existence as described in the Bible seem impossible, you'd have immortal turds, as if they're living creatures. Bizarre.
>>you’d have immortal turds,
You’re the one claiming decay didn’t exist prior to the fall; and sans decay, immortal turds is exactly what you’d have.
Now, back to the biological carrying capacity of your “perfect little biosphere”.
Was the Earth the same size then as it is now?