I think that we make a mistake any time we look at our own experiences and try to generalize out to humanity. One person could say, "I can't get over my jealousy, no matter what I try, so jealousy is innate, and polyamorous people are just fooling themselves when they say they're happy." Another person could say, "I got over my jealousy with a little trying, so jealousy is just a construct and monogamous folks just aren't trying hard enough." (Please note that I don't mean you're saying that exactly, OP, but some people do take it that far.)
Both would be wrong, though, because they're assuming that their experience can act as a stand-in for all of the human race. Certainly we can learn lessons from our own lives that can help some others, maybe even many others, but rarely, if ever, ALL others. In this case, for example, I would say from my reading and observations that jealousy is real and natural, and maybe impossible to let go of for some, non-existent or easy to let go of for others, and most are in the middle of those two extremes. They feel it as a real thing that does exist, but can let it go with some time and work.