I don't see why it should increase reaction times at all. If I do need to brake then that's all I do - whether CC is engaged or not is immaterial.
Like everything else it can be a useful tool.
That report is indeed interesting. Just how could the car be going through the air faster than the speed set? If the wheels were in fact aquaplaning then they would sense the speed as being higher than it was and take the throttle off.
And aquaplaning? If your tyres are in decent condition there's no way this will happen unless there is considerable standing water - not merely "raining".
Actually if you read further down the report much of this is said.
Another case of soi-disant experts telling us to ignore the rules of physics.