I understand that LED headlights are supposed to be brighter, but I'd like to know how much brighter? Like 10%, or 50%, or 100% (twice) as bright, for example?
They are supposed to be brighter - truth is, they are not. As Altin already stated: get a good xenon bulb and you will easily achieve more output from the headlights compared to the LEDs.
The adaptive curvelight is also included in the advanced xenon headlights. So it basically boils down the the different look. The LED headlights also feature LED turn signals as opposed to the halogen turn signals on the xenon headlights with the LCI. Pre-LCI models have LED turn signals with the xenon headlights.