Kollel is a siman, not the sibah.
How so?
I don’t think Chassidim are much different in terms of divorce rate, perhaps even a bit worse, and you can’t take a control group from a different era, because there are too many other factors, mostly the overall moral decline of society.
Point is, your assertion that there’s some type of correlation between kollel and marriage issues is an invention of your own with no basis in reality.