Confirmed, the ambient mode is now really an ambient mode. I have not tested it but for a few minutes so far. I expect it will chew through the battery pretty quickly, even though it looks like the backlight is kept at absolute minimum brightness.
Ambient mode was only really designed for OLED screens or transflective screens, not screens with an active backlight like the Moto 360.1. In fact it is pretty useless on an LCD with backlight like the Moto 360.1- with the backlight on min, the screen can't be seen in daylight at all. I suppose it could still be useful for night-time if you needed the display always sorta-on.
Now, it could be a change in preparation for the 360 sport, which might benefit from it and they wanted to keep the software the same. Just some speculation.