Yes, this is a disturbingly common pattern. It's rare that I have ever seen a WAS truly upgrade. There's exceptions of course, e.g. walking away from an abusive relationship. I wonder what it says about your W's self-esteem? It's really sad when I think about it.
I feel this, too. I know enough about the OM in my sitch to constantly think to myself every day, "Just what exactly does she see in him?" It's hard to know exactly why this is such a pervasive pattern; I sometimes wonder about it. My guess is that "downgrades" are easier to ensnare and mold into the great A fantasy than "upgrades."
Keep on keeping on, Tele. You will find the love that you deserve one day.