Actually the 2x zoom is not an optical zoom. It's a crop from the 20MP sensor, colored from the 12MP sensor@dov1978
The longest exposure time is 30 seconds.
I believe the dual cameras are more for sharpening and true HDR effects.
The Mate 9 also has an optical 2X zoom with hardware stabilization which functions very well.
I've no experience with a Lumia 950.
Those Lumia cameras are hard to beat however.
WOW these are great low light shots! Was this in manual mode? Low light is one area I find the Mate 9 struggles in with the f2.2 lens.
Do you have the raw on that one ? It would be interesting to try and pull tg the blown highlights in.