I think there's a world of difference between saying that "the current approach is counterproductive and could be improved" and "it's all the police's fault". If you are arresting people and not charging them at the levels apparently seen, ie about 60%, that's rather too high and should be looked at. Why are these arrests not leading to charges? Not enough evidence? The evidence that is available is not admissible in court? Or is the evidence that led to the arrest just plain wrong in the first place? Not sure, probably a mix of these.
One way or another, it seems to me that there's a case to be made for more effective police actions against potential terrorism, whatever that means. But no. I absolutely do not see this as meaning that the police are at fault. Even if it does drive people further into radicalisation when they are arrested and then released, it seems to follow that such people must have been heading in that direction anyway. The arrest was then a catalyst but absolutely not a cause.
As to misrepresenting the threat, I suppose it's a risk of relying on language. I can believe that the threat is severe and real. But at the same time it's also fairly small, in comparison to, say, road deaths. I don't think that makes the threat not "severe", though. It only takes one Paris-style incident to justify that description.