Extremely weak and just within few levels in D4

So I need some help with understanding what is going on in D4. I am a level 50 necro and I have 30% resistances and about 450 armor and I am playing on expert tier currently. When I arrived into expert that was about lvl37 I was NOT getting one shot, my survival was good. Since then I have done what I suppose to upgrading my gear with exact same legendary gear and I was able to stand in boss mechanics at around lvl45. I have upgraded my gear further and now at lvl50 only now I am getting one shot by anything that just looks at me regardless if there a boss or petty flies.
I know I need to improve my armor and resistances though given it was only 2-3 levels difference from great to pathetically bad feels like a bug or something.
Saying this, last season (S6) this happened to me when I created character on normal tier and when i moved up into hard tier the same thing happened. I ended up resolving this by creating a new character on hard tier skipping normal, and then I was perfectly fine and I never had a problem like that on that character again.

On the diablo ONE forum???