It appears to me that it was the PlantEverything mod that was actually skewing the drop rate.

To answer your question, I do not believe that "damage dealt" has anything to do with "items dropped", either in number or in contents. It's also entirely possible that one of your other mods is adjusting either or both of those, even if PlantEverything is removed.

I would suggest removing all mods entirely, if learning about base game mechanics is the goal.

All of that being said, I eagerly await the results of your testing; please keep us posted.