I made Greater Rift level 60 with my Necromancer last night with the Inarius set build. I had more or less optimised my Necromancer with the right items and powers.
It is probable that I can push for another 2-5 levels. I will see tonight.
Meanwhile, I had optimised my Rathma set build further and pushed it to GR55.
I had prepared and planned for the Necromancer for a while now based on what little I know, that of it being a class based on the intelligence attribute. This had allowed me to progress swiftly to acquire four full sets in a matter of days. It has also allowed me to progress swiftly to GR40.
As for allegations that the class is overpowered, it isn't. It is easy to build, easy to play, easy to progress in the intermediate GR levels, however, it might not be easy to achieve the higher GR levels. In the rankings, the best Necromancers are hitting GR104 which is a bit short of the Wizard's GR106 or the Witch Doctor's 107 for 2017.