First of all love the game, couldnt ask for better in most areas. Second, fantastic job on the end game bosses.
That being said - I think he should be quite a bit harder. I was lvl 83 and dusted him on my first attempt. The lvl 68 timeline boss was very tough and felt end game enough for me.
Also - some cold damage uniques from end game? Stuff for the other classes looks amazing.