Both stats reduce damage independently. Therefore, the best bang for the buck is to balance them. But we start at different base levels, so we have to take the relative efficiency into account.

But defense is non-linear, so this relative efficiency will depend a lot on where your champ lives in total power level. Higher levels should be more HP-skewed. A build (at some fixed power level) is balanced if the derivatives of the survivability added by each stat equal each other. By survivability I technically mean "raw damage resulting in a lethal hit".

To make things worse, there's flat stats to consider. With artifact ascension and accessories, there's some flexibility in how you go about obtaining each stat. For a low base stat, flat bonuses are more efficient, relatively speaking. That makes the whole problem multi-dimensional (we have two incompatible currencies to "spend", can't just abstract it into a generic bonus% to be freely allocated via main and substats).

Anyways, it's definitely possible to write an algorithm computing the optimal point, and I guess the hellhades optimizer already incorporates something along those lines.

Huh?

The damage equation is:

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Real damage = Base Damage * (1 - 0.85 * (1 - e^((-2 * DEF) / 3000)))

Suppose you were to use a champ like Arbiter as an example, who has a base HP of 21135 and a base DEF of 1101. Suppose we were to evaluate the effectiveness of adding a single +60% DEF glove vs +60% HP glove, at different HP/DEF values, the two % HP Remaining columns will be when hit by an attack that does 20000 damage, before reduction:

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Now suppose you were to instead use a champ like Hurndig as an example, who has a base HP of 16020 and a base DEF of 1101:

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And, lastly, suppose we took a champ like Tuhanarak (base HP 21645, base DEF 1277):

i

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....so....bright.......

Thank you. I'll try to replicate it with the same HP, just focusing on damage dealt proportional to increasing defense when I have time. HP is fairly straightforward, it's a pool from which damage dealt is subtracted. I'm going to try looking at the damage mitigation portion of the equation more closely.