What? I've had no problems, nor do I know of any other 8th gen in my area (or 200km radius) that has had any problems with changing the rear sway bar to either the SI or Progress rear sway bar. Without changing the control arms. (I drive harder now than I did before)
How many instances have there been? what stresses were put on the break point? Were the parts lubricated and installed properly?
Just my $.01
If you're basing the failure of the non si, with the non si control arms, it's not the control arm that failed, it's the metal of where the mechanism was that gave way, a defect of the metal under the stress of the sway bar / control arm.