Thom makes some very good points.  Nikon AF also has a strong closest subject and high contrast bias.

• I would have used AF-C Wide (L People) release priority and burst 3-5fps. Bursting improved my ML results, and I wish I had done more bursting with my D500 as well.
  
• I also would use 3D AF-C with the subject selected "marked" as it is intended to be used.
  
• I found Z8/ZF face detection to be less detective than the II's, but better when it did detect.  You can experiment with it using photos, TV, and other videos.  This way you know what to expect.
  
• Your subjects were backlit and the eyes were in shadows.  That usually means spot focus and metering, and possibly even EVF exposure off, as recommended for flash and studio photography.
  
• With F4 glass I don't need eye-level detection, and I wish Nikon offered a simpler face only detection option as the Z5/6/7 offered.  This would also make it easier to switch between subjects.

As you're experience it is better than the Expeed6 bodies, but not quite up to the Z8/Z9 experience.  Competitors $2,000 systems are less restricted.  I feel like the ZF is more of what the Z5 should have been.  I also feel that the ZF/Z8 are a bit over priced, but the competition's flagships are still more expensive with other drawbacks.

For enthusiast/family shooters there is still up for grabs.  The right DX body could grab these users, and the Sony/Canon APS-C releases didn't have updated sensors.

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