After the latest patch, the Borg healing structures no longer heal properly. The gateway in ISE doesn't heal and can be killed- even on elite difficulty- before the transformers are taken down. In CSE, the cubes can be killed without their transformers being knocked down first.
Oddly, the secondary healing structures still seem to heal- for CSE you still need to take out the nanite generators in proper order- but you can knock the cube out directly. In ISE the same applies to the nanite transformers.
I haven't tested this on KSE yet, but 2/3 suggests that similar holds true for it.