Sorry, are you saying that it was the two 'inhumane and evil women' who are responsible, or 'the people employed to do their jobs and failing miserably'? You can't have it both ways, even in an attempt to let the people cutting funding to social services off the hook.
Yes, the women are absolutely responsible, but it is arguable that Smith should have had support from SS because of her IQ. I'm not sure how they would know about her before the problems started, though - I assume that they'd only find out after something had happened that made someone report. In any event, support would be far less likely to have reached her than it would have if there had been proper funding.
Yes, Star was failed by SS, but at the same time, SS was failed by the government. There are only 24 hours in a day, and only so many hours in a working day. If there are not enough social workers they simply can't get around all the families on their books - it's not complicated. If there is not enough money to pay for more social workers, this sort of thing will happen again, and the more the social workers are blamed, the more will leave the profession and there will be fewer new entrants.