"Jealousy" needs to be unpacked.
I agree. My definition is as follows. Jealousy, unlike envy, where you want what someone else has, and possibly resent them because you do not, is the want to restrict the other person's thoughts, actions or choices to prevent some real or perceived harm to yourself.
Jealousy as a smoke alarm
I agree with that. Though my guess that there are more accurate fire alarms out there.
OTOH, I suspect that even in a polyamorous, compersive context, a total absence of jealousy would cause relationships to drift apart a lot more than they do today
Quite possibly, if there is no other feedback available. But first, I am not sure that it is a bad thing. People change and polyamory goes some ways toward making the relationships change with them, rather than becoming a burden. Also, I suspect that compersion does not equal "no-feedback", though. Certainly healthy parent-child relationships tend to be compersive, with plenty of feedback along the way.
Sometimes our minds suddenly "click" and we see a topic in a new light. Or sometimes we think we understand an idea, think it's stupid and ignore attempts to explain it ("yeah, I already know that"), until we suddenly realize that our understanding was wrong.
This kind of insight is supposedly hard to transmit, but it might be worth a try!
So, what kind of important and valuable insights do you wish you had earlier? Could you try to explain briefly what led to the insight, in a way that might help others get it?