That’s probably right in general, but:
“The nine-month study involved college students who had been dating at least two months who filled out questionnaires every two weeks.”
I think break up can indeed “feel that bad” sometimes, especially if you talk about couples, who divorce after living for years together and raising children. College students, who haven’t had yet enough time to buy a house, raise children and live for years together, aren’t a suitable group to make such experiment on, unless you want to talk about relatively short-term relationships. What’s 2 months or even 2 years without taking all kinds of responsibilities on yourself as a couple compared to f.e. 5 years of marriage?

Also, a good point about “anesthesia and real recovery aren’t the same thing” and feeling pain even years after the break up. Again, I believe it’s especially true for long term couples. Divorcing after having children makes it worse too.