Boss fights and The Vision

I understand that what is referred to as "the vision" of devs is mainly to incorporate in POE2 skilled combat for boss fights. This currently seems to be turning into a competition between players and devs, where the toughest bosses are dealt with not by skill but with power creep, and devs answer with devastating one-shots and more HP.

To understand what is going on, we should compare to some models of games that mix builds and skilled combat, such as Dark Souls and Hades. One striking difference is that these games have very few means of recovering life: estus flasks are limited, life is a rare and precious thing in Hades. There are no or very few one-shot mechanics, because they are not needed to create a challenge: players are allowed a certain number of errors, but not too many.

However, POE2 cannot forego recovery, because it is good in mapping and part of the identity of many builds (leech, recoup, ES recharge, ES leech, etc.) My suggestion is to give the most powerful boss attacks a new stat "x% of damage is reserved" which applies to all health pool contributors: life, energy shield and mana. Typically, x could be around 0%-5% for boss skills that are used often, up to 20% or even 100% for the most telegraphed, rare attacks. Of course, this should go with lesser damage overall, so that to a mid-tier build the challenge stays approximately the same. This will make bosses untankable, and avoids using one-shot mechanics to create challenge. These reservations could be removed at the well (or better, by returning to town, having to go the well is a bit annoying) to make the mechanic viable for both arena and open-field bosses, or when the boss dies.

This does not address the power creep, and may push players to wait until they can one-shot the boss before engaging it. This can be solved by adding a "boss ward" which would provide damage reduction in term of the amount of life lost "recently". More damage faster should always be better, to avoid a clumsy play style where we wait the ward to go off before attacking again, but with diminishing returns. A possible mechanic could be that each damage taken adds some value to "ward intensity", which decays exponentially (the more ward intensity, the more damage reduction, with diminishing returns; and the more ward density, the more it decays so that in permanent regime there is a monotonic, though not linear, translation DPS <-> life loss) ; and hits are decomposed in small chunks so that ward intensity gained from the first chunks apply to to the later ones, in order to avoid one-shots and not to favour big hits at a given DPS level (this could be tunable if devs want for some bosses to be easier or more difficult for big-hit builds or many smaller hits ones). It would be easy to tune this to ensure that each phase of a boss fights lasts a minute or two at the minimum, making players engage with the mechanics.

Even if the details necessitate much tuning and more thinking, I feel that there is a way along these lines to fully achieve the vision, which would make me enjoy the game much more!