I just duped him recently but I have seen videos and still not convinced to take him above 3/5.
I have my 6* (duped) at R2, and I enjoy playing him quite a bit. He can shut down robots with his Armor Shatter, has great power gain and armor breaks, the coldsnap ability is still something that does not have too many counters. He is a solid AW defender, too. I have no regrets taking him up, and actually do end up using him regularly in various content. I'd love to see some immunities for him, but that is really the only thing he's truly lacking IMO.