This is comparing abusive homes to marginal foster care children, which means children that were repeat care kids, meaning that the failure was not in foster care, but in the decision to reunify and then have them return to care. The success rates for children that are not intervened early or that are reunified are terrible, and research like this edge case for a PHD are the exact things that get kids reunified that should not be.
Also: if the success rates for these kids are so low, then why intervene at all? Surely not doing anything is better than what this paper describes in terms of outcome. Or I should say: that's exactly what this paper says: no intervention is definitely the better option for the kid. And given that these kids end up in prison, it is the better option for both the victims of the crime that lands them in prison and for society that has to pay for it. So why intervene at all?
https://sci-hub.se/10.1257/aer.97.5.1583
The result is that by every metric, from reading scores, to subjective and third-party assessment of happiness, to years of study, to taxes paid (which means how much money they earn as an adult), kids left in "abusive" homes do better than children helped by CPS. Other studies point out that this applies on every point on the spectrum, even when the children simply receive psychological help at school or other less invasive things.
A very significant group of them develop "Reactive Attachment Disorder". And ... well, just read:
https://en.wikipedia.org/wiki/Reactive_attachment_disorder