You would think that (oh the curse of knowledge!), but there is still something that muddies the waters here. It is the missing relation between the physical el

You would think that (oh the curse of knowledge!), but there is still something that muddies the waters here. It is the missing relation between the physical electric field which is what the free charges actually generate and the (still mysterious) displacement field. This makes your explanation more abstract that it needs to be. The "D = E epsilon" that you mention in passing is in fact another source of confusion, because it is not clear whether E is what the free charges ("q1") generate or it is what acts on the probe ("q2").