AT&T needs plenty of time to make sure that the update which fixes these problems also has its own new severe flaws, Apple won't allow the update to go forward any other way. Can't have actual competition, can we? The horrible quality of AT&T firmwares for Android phones is clear evidence that AT&T is bowing to Apple's every desire.
None of the problems with UCKH7 (Data-eating AP Mobile widget, lockscreen issues) were present in any I9100 firmware I know of.
All of the problems with UCKK6 do exist in various I9100 firmwares, but never simultaneously in one build. UCKK6 is the ONLY Samsung firmware where Bluetooth HID was broken even when using the stock kernel. (Samsung made a change that required kernel updates, and did fix I9100 stock kernels, however they never released source code for the I9100 changes.)
Samsung clearly has fixes - just look at XWKL1 for the I9100 as an example. It has, as far as I can tell, none of the problems UCKK6 had, and was built not long afterwards. I've only seen the BT-AMP bug crop up once on XWKL1, and that was when I was conducting a very aggressive experiment in the kernel, since reverting that experiment out it's been rock solid stable.