Should the backweel of shimano R520 wheel look different than the front besides the cluster Iow the alignment is not in the middle?

Answer 1

Rear wheels on bikes with external gears should look different.

(Unless you've got one of the very rare frames with an assymetric rear dropout)

To make room for the stack of sprockets that gives you the different gears, the drive side flange of the hub is shifted closer to the middle of the axle than the non-drive side flange.

But you still want the rim to stay centered over the axle.

So by running the drive side spokes at a sharper angle, you get the rim to sit centered over the middle of the axle, even if it isn't in the middle of the hub.