Getting One Shot With Max Resistances is not an ARPG Game

The only thing that actually one-shots (and other than pinnacle attacks like Arbiter) in 0.4 are red slams from high-tier map bosses and powerful rare-mob slams which have been juiced up with damage+crit modifiers. It is possible to be unlucky but most of the time it's just run-of-the-mill critical strike/damage modifier stuff paired with missing a dodge roll or letting yourself get wheel-slammed or something else skill-issue related. Dying to a skill issue sucks but it's definitely not unfair.

What I see happen more often that feels like being "one-shot" is from people who are not prepared for burst damage in any way whatsoever, or those who also don't understand things like shock/stuns, or they blindly follow the ES meta on characters who would benefit immensely from having ar/ev/block/regen/etc.

These ES-meta-slave scenarios are famous for "one-shot" clips.

They all pretend they are masters at manually dodging everything so they should only care about max-hit rather than sustain, and will get chunked for 1/3rd their ES, become shocked, and then get deleted by a critical strike or a bunch of stacked AoE hits shortly after, maybe with one large hit from a rare that makes it look like the rare was responsible for an unfair one-shot.

It's usually the case that a player that dies to a huge amount of burst damage from many hits in quick succession while having nothing but a ton of ES would probably benefit from an alternative and more complementary defensive orientation. They'd have a lower number in terms of "max hit" but it would have resulted in them blocking half of the hits, evading the next quarter, and mitigating the remaining quarter with armour/deflection while rerolling any crits to normal hits and they would also likely proc other defensive bonuses to further mitigate and provide enhanced defenses for any more hits while they recovered as they would be 'hit recently', 'blocked recently' or perhaps on 'low life' rather than 'dead'.

But everyone holds up that 'max-hit' value from PoB that they get from stacking ES as if that's the holy grail and the only way to avoid 'one-shots' - this is only true for red boss slams and the odd juicy rare-slam, and even then it's only good if you get insane amounts of ES (>10k) which is difficult (but not impossible) to do if you also want more than one useful layer of defense, which you should have because the odds are you don't have Ben-levels of manual dodge capability to compensate.