The "laissez-faire" and "arty-farty" stuff is simply a stereotype based on no knowledge of what actually happens in these schools.
I am aware of their shortcomings, and, as always, favour looking at your child as an individual and deciding whether this system is right for them. My 3 children went to 3 different schools based on their strengths/weaknesses and personalities. A Steiner school might not be right for many, especially in the upper school where some children feel the need to move away from the system, which is what my DD2 did. It was right for her when she was there, then something else was right as she got older. I do not see that as a good reason to damn the schools out of hand and certainly not in the absence of proper knowledge.
I have tried to explain that the art aspect of the system relates to not making a firm division between art and science, but seeing both as being inextricably linked. Understanding a scientific concept need not be in isolation from the awe and wonder we might feel at these concepts, and art and poetry are part of the science curriculum. And lower down the school the art is integral to what the children do - and is not based on whether someone has artistic skill - the processes used are simple and allow every child to achieve satisfying results.... wet on wet painting, use of large crayons and blending colours. My 8 year old GS came home in tears from his state primary last Friday because he had "failed" to do a task in his art class - what in heaven's name is that about? I am sure that by these parameters, Picasso would have failed spectacularly! Children in a Steiner school engage in art because it is satisfying and creative, not because they have a set goal. in Maths "carrying" numbers when adding involved them drawing with coloured crayons a cross-section of a barn and carrying sacks of grain into the loft are when one side was full. How much more imaginative and helpful is that than the printed-from-the-computer worksheets that my GC come home with? Learning through doing is a long established fundamental of pedagogy.
You are happy GSM to damn this system whilst having no experience or knowledge of it, and without comparing it with what else is on offer - i.e. the state system and the ways in which this fails so many thousands of our children, and destroys teacher enthusiasm.
I think both systems have their virtues and their problems, but I hope we can try and be objective and not just condemn either out of hand without looking at them in more detail and with an open mind.