The true damage is caused by societal and economic overreaction from the target: fear leads to expensive security theatre, a desire for vengeance leads to lashing out with expensive unnecessary wars, uncertainty and political instability destabilizes financial markets, etc.
Some diseases are similar: immune system overreaction causes more harm than the actual invader.
I don’t think that’s correct, and do not see that Wikipedia page say that. It says
“The purpose of the weapon is to contaminate the area around the dispersal agent/conventional explosion with radioactive material, serving primarily as an area denial device against civilians.”
I think that “serving primarily as an area denial device against civilians.” isn’t 100% correct. For use by terrorists, I think it’s more to instill fear than to make areas inaccessible to civilians (that still would happen, but isn’t the goal)