I think 1.6.x is stable in so far as basic flying goes and is probably the most stable given that it's had the most updated and improvements.
I imagine that some people not upgrading are doing so because of (as you say) reduction in terms of functionality, not stability. As far as I know, there is one subject of contention (someone help me out here -- I'm forgetting the official name of this): that restricted permissions thing functionality where you need permission to fly in a zone (not the red No Fly Zone, but the yellow "must acquire official permissions" to fly there).
If you see those zones on your map, it's probably an area of concern for you. I don't see any, but that doesn't mean that hey won't appear in the future.
Note: that one restriction mentioned above may also be DJI Go app enabled. It may be just that, just firmware, or both.