To me it QT temps depend on species, and what their natural temp range suggests.
A cichlid or tetra from Uruguay, or northern Mexico might do best in the low 70s, but a cichlid or tetra from Panama may do fine in the low 80s.
Another consideration are the bacteria different species have built, or don't have resistance to.
The bacteria that causes columnaris becomes more virulent at temps of 80'F and above, so subjecting a fish to higher temps than it has evolved o live in, after the stress of shipping to higher temps than its natural range could be counterproductive.