A good friend is a Legal Aid solicitor who acts for parents where the LA have 'instituted proceedings'.
She has been doing the job for 20 years or so (sadly, has on a number of occasions been asked to act for a mother/mother-to-be on the grounds that she was the solicitor for the woman's parent when the LA was taking action over her as a child).
I did ask her a while back whether she thought the LAs in her area (her firm covers a number of London boroughs) were too quick to take action. She was very clear that in 20 years there were a handful of cases where she thought the LA was wrong to start proceedings, but in each of those cases it was a borderline decision and they weren't being completely unreasonable, just should have given the parent(s) a bit longer and another chance.
But in none of that handful of cases was the LA being completely unreasonable - after all, in the end the LA applies to the court for whatever order they think is appropriate, and it is the judge that decides. The SWs make the case to the LA lawyer, who decides whether to make the court application. The case then goes to court, and the parent(s) have Legal Aid to get proper legal advice (in these cases Legal Aid is not means tested).
And a number of her clients have been successful in opposing the LA applications - in her view for some people the LA making the application was the push they needed to take the situation seriously and make the changes their children needed. In the majority of cases where a child cannot stay with a parent they end up in a kinship placement i.e. within the family.
Having said that, some LAs are better than others - some have been ranked as Inadequate by OFSTED and some publicly criticised by judges for their poor standards and decision making.