How you play this game as melee HP based in end-game content?

They want you to actually dodge boss attacks. Armour is good for mobbing at minor boss attacks. GGG wants you to slow or immobilize bosses, increase attack speed so that you can weave in attacks, etc. They don't want you being stationary using Fury of the Mountain for the entire boss fight while tanking every hit. That attack has range on it so you can sit back and let totems slam the fissures while you regen when stationary, cast spells, then go back in. Oracle is fine imo. Defense from an ascendancy is not mandatory. It's actually possible to completely forgo defense on a melee character if you're patient and play well. You learn bosses and punish with an attack you know will be able to land in that window of time. If this is not fun, then switch to a caster. As a melee, build for permanent stun and use slows.

A fellow PoE1 vet here, I played many life-based builds into the PoE2 endgame in hcssf before I ever touched a character that used ES just because I tend to prefer strength attribute based skills/playstyles.

I've been into the mid-90s many times and what almost always kills my character is a large, singular critical strike or big boss slam on a map that had damage modifiers - things like chaos damage and shock sometimes playing a role.

I decided to switch to ES, ES/EV builds for a bit to see the other side of the coin and after getting just over a handful more characters 90+ hcssf using this defensive aspect, I will say that while it is easier to get ES numbers to a point where you can eat large hits, you definitely do not do as well with sustained hits. And unless you are CI, chaos damage is just as deadly - maybe more so. There is also a higher vulnerability to DoT and ailments that needs larger investment to mitigate when you are an ES-centric character.

Comparatively, the defensive benefits of ES vs life seems to be situated more around playstyle than they do around which one lets you take a bigger hit.

The life-based characters can usually have a playstyle that puts one right in the mix of things, unafraid to risk errant hits here and there from white, blue, or occasional yellow monsters with some exceptions, so there is a higher demand for hit-pool recovery and/or avoidance/mitigation.

In the endgame it is not difficult to build warrior that can stand in the middle of a dangerous pack and AFK even with some dangerous map mods, and it's typical to get ~2.5-3k life and have significant recovery/recoup and usually something like block to supplement.

If you're not going to use a separate layer like block, you need to compensate by having some mix of increased hit-point pool in the form of more life/es, and a way to recover that hit-pool, whether you are pure life or hybrid life/es. Things like WitchHunter Sorcery Ward, deflection, and evasion fit into here as well.

Overall I find that when doing a life-based build that does not have any or much evasion, even if it has ES, I need to invest into crit damage mitigation/reduction and something to deal with shock, and depending on the amount of block/avoidance, it will dictate the levels of subsequent investment into recovery, more es, es recovery, damage taken as another type, etc.

ES builds actually still need to have the same level of investment to feel tanky - a lot of points are used for stun/ailment threshold and increased ES. Point-for-point, it's not actually any less, but I would say that it is more intuitive/simple.

I think the reason that ES "feels better" to most people is mostly related to playstyle and the simplicity. Both styles are gear dependent but I would say that ES-centric styles feel a bit more gear reliant in the early endgame compared to gear for an Armour/life-based up until the very lategame where they seem equally gear-reliant.

I do think it's the case that for every life based player that dies to a "big slam" from a crit, damage-enhanced t15 boss slam that a 10k ES player would have been fine with, there are likely 10 more ES characters that never make it past tier 5 maps because they are weak players who can't avoid hits or are unlucky with a quick succession of hits.

Those same weak/unlucky players might make it through farther on a life-based character, only to get 1-shot back to the beach by a mis-timed slam dodge if they don't have the "extraneous" levels of investment into things like flat physical damage reduction, crit damage reduction, extra elemental/chaos defense past capped resistance, etc. that are required if you want to make life-based characters have a similar level of "mega-hit defense" that ES can achieve with decent gear and some points.

This also means that very good players will see a larger advantage in being able to eat an occasional mistake, as their enhanced playstyles allow them to avoid most damage mechanically in the first place - the inherent disadvantage of recovery associated with ES is less present because they are mechanically better players. This same sentiment applies to OP builds that delete the screen and circumvent any need for mechanical skill to begin with (but that is a separate topic).

So in effect, it's "easier" to get to the endgame with life-based characters but "harder" to stay there once you're there unless you want to grind out all the extraneous investment you need to be on a similar level as someone with 10kes who uses range to remove everything except the tankiest of rares or bosses before seeing any threat to their hit-pool.

Very good players will always prefer the ES-centric route because they get to avoid dealing with a lot of the "extraneous" investments that a life-centric build would need.

This will also be preferred by players who consider themselves "very good" but are really just carried by OP builds because they'll switch over to a life character after playing an ES one to level 90 and then get one-shot over and over by both campaign and map bosses due to mechanical weaknesses while they blame "the build" or "melee" or "life" and hold up their level 90 ES characters as proof that they know what they're doing and the game is unbalanced.

There are other forms of pseudo-defense in the form of crowd control mechanics to consider as well, but I think I've covered the main "ES vs Life" points.

It is simple, they want you to play a ranger, just look at what people are playing, pathfinder is still highest % played yet they nerfed warrior league after league. Armour is by far the worst of defensive options, range can just expload the entire screen, not be there as they get more movement and the range makes it much easier to manually dodge, or if all else fails rely on ES/Dodge. The devs either dont want to see it or just dont care.