I didn't agree with this on FB and still don't. The violence gets to a definite peak of horribleness in Ep 4 and then settles down to an acceptable level of brutality:-) ( except in one fight in um , ep 8? Which is sufficiently interesting to justify itself I think).
In fact the then showrunner Steven de knight ( ex Angel, natch) gave an interview in which he more or less said " we pushed it as far as we thought we could to end ep 4 and then we thought we'd better stop".