You don't need root if you have to ask why.
What's the big deal about the camera????
They simply expected DSLR(or SGS8 at least) camera quality, 4K zero-bezel display, IP68, Iris scanner, ... phone for 1+1 price. And now they got 500€ phone which isn't better than 900€ ones....
Try to cover zoom camera and shoot photo with 2xzoom - only main camera will be used
Not true. In bright conditions secondary camera is used. You can check it in EXIF.
There is no problems at all. You and OP just have no knowledge about batteries and speculate about problems which doesn't exist. This is waste of time, look at spec sheet of battery: Nominal Voltage - 3,85V, Cut-off voltage - 4,40V. Case closed.
Another two. I'm pretty happy with camera. 1+ simply overhyped this and it really pissed lot of users, but for its price it is decent shooter with potential to be even improved in future.