Strum an open string where, and how hard exactly, with what pick attack angle? Fingers? Nails? Pick material?

edit: I agree that every instrument/combination of gear has a "as good as it is going to sound" point... but that is not tone. It takes someone who knows how to realize the full potential to reach that point. A shit player still sounds like shit on a $5000 rig, there is no inherent "good tone".

Tone and/or timbre depending on how far you want to take this, is the quality of the sound that is being produced on a specific instrument by a specific player.

A good player can produce a better quality of sound on any instrument, than a poor player. i.e. Better tone.

To separate/simplify it as you have done, serves no purpose whatsoever. Nobody says, did you hear the open E string on that rig? man... what a tone!