Fgs we leave pups with their bitch for 8 weeks.
Well, sure, so that they can be taken care of. The baby is going to get taken care of too--by the adoptive/genetic parents. Nobody is going to be abandoning the baby.
The (admittedly somewhat limited as of 2020) data which is available on the long-term psychological outcomes of kids born through gestational surrogacy, suggests that they turn out just fine and have psychological profiles comparable to children born in the "regular" manner. Of course, this could change as the kids get older and as the pool of surrogacy-born kids grows, resulting in a larger amount of data. So far, however, there are no particular reasons to worry about the psychological health of surrogacy-born children.
academic.oup.com/humupd/article/22/2/260/2457841
www.today.com/health/new-study-tracks-emotional-health-surrogate-kids-6C10366818
I think the concern about "bonding/attachment will cause psychological issues in the child" is coming from the observation that adoptive children in general (even those who were adopted at birth) have high levels of behavioral and psychological issues--but there are much more probable causes for these issues and none of these causes is applicable to most cases of surrogacy.
We no longer live in an age when psychologically normal, bright teenage girls regularly give up babies for adoption due to unexpected pregnancy, so babies adopted at birth are usually being adopted out due to their being removed from their parents by court order--typical reasons being drug addiction, alcoholism, neglect/abuse or older siblings, very low IQ/serious mental health problems that can't be managed or treated, or having parents who consist of a violent and dangerous man and a woman who refuses to leave him or keeps forming relationships with other dangerous men. If the genetic children of people with these kinds of profiles have high rates of "issues" of various kinds, I am not going to collapse in astonishment, let's put it that way.