Did the game force you to play at master level? Do you still need to run around with 90% health when you have 500 maximum health? According to the existing game system, keep being 1 hit kill means either your build problem or your gear problem. There is an option to lower the difficulty, please serve yourself.
That's why many players asked for a kill move toggle, and i like that idea too. When there is toggle kill move then you can just play what ever low health build as you wish, fair enough?
Lowering the difficulty is not the answer, because it doesn't address the faulty mechanic. The problem is not that we're getting one-shot, it's that the means by which it's determined that it happens is using the wrong order of operations, which is negating any and all forms of mitigation.
There's a huge difference between getting one-shot because you screwed up and having it happen because the game decides to randomly screw you over, and the latter is what's happening here. Master level exacerbates the problem, because enemy damage is artificially amplified, but it can happen on almost any difficulty setting due to the faulty mechanic behind it.
The only aspect of gear or build that matters in the slightest here is how many times you decided to increase HP at level-up; this basically results in forced selection, which is considered bad design and nigh-universally panned when discovered.