The rotation in world space will give you the rotation in world space. That’s totally expected. If you want to get the difference in rotation, you can simply store the object’s rotation in world space inside a rotator type variable before rotating it, and once it’s rotated, compare the stored rotation value with the actor’s current world rotation by using the Delta Rotator node.
However if you’re smoothly rotating an object and comparing it’s current rotation with a pre-determined starting rotation, to continue getting positive values (181 instead of -179 for example) you can update the stored rotation and after every comparison with the current rotation, you can add the result onto a float type variable (or rotator if you want to get all of the axes)
Hope this helps! 