I think there is a solution to the one-shot problem that would elegantly address both the “instant jumps to full health so only one-shots matter” and the “regen can’t compete with leech” problems, but I’m guessing engine might prevent it from happening. And ironically, as much as I also enjoy GD way more than PoE, PoE has that solution: make lifeleech happen over time, not instantly.
In an environment where leech is instant, there isn’t really a way to make attrition-based combat where enemies take some health away and you need time to recover it. Leech or our damage would have get nerfed hard and enemy damage would need to get nerfed hard. Our health pool relative to enemy damage would need to be fairly massive so that we can have chunks taken out of it, not be able to recover all of it instantly, and still be able to survive the next series of hits. And our damage would need to be low enough that everything doesn’t get blown up after it gets to do 1 attack, cause then the attrition doesn’t really happen. That’s the PoE problem, the whole screen gets blown up in one click so for enemies to be dangerous, they need to hit insanely hard cause only like 1 out of a 100 gets to actually attack. An attrition-based combat would probably require a full redesign of encounters and the overall flow of the game and it’s questionable whether it would be worth it, cause there’s a good chance in the end it would feel worse than what we have and all that work would have been wasted. And also, we’ve seen what happened when leech got nerfed in raw numbers or sunder got introduced. People just got more leech, builds just got tankier, and ignored both.
With leech over time, though, enemies could move away from the one-shot threat territory and more into wearing you down over time because even if they don’t one shot us, they can pose a challenge to our ability to leech back quickly enough to survive the next barrage. Kill speed would still equal defense since you thin out the enemy horde faster and mitigate more damage, but it wouldn’t necessarily mean more survivability in terms of the ability to take damage, not if, like in PoE, there were a cap to how quickly health can recover from leech (as in, you can’t be leeching more than X% of your max health per second). Because then, you can’t solve the issue by getting more leech, it won’t change anything. At most you’d be able to get more health so the % of health recovered is a higher number.
With that, leech would be much more comparable to regen or health per second heal mechanics because it can never just get us back to full instantly. But I assume that’s dream territory cause GD probably doesn’t have the capability to incorporate over time leech and leech caps like PoE does.