The title sums it up. While it is true that ailments are often soft-locked behind certain damage types (e.g. the Mage passive tree having nodes that only grant Fire skills a chance to Ignite, Cold skills a chance to Chill, and so on) & certain Skills (e.g. Fireball has nodes related to DoT damage and Ignite application), I nonetheless am left with the feeling that Ailments and their applying Hits/DoTs are not tied closely enough together: there is something thematically wrong with there being no inherent maluses to Igniting someone with a primarily Cold hit, and no inherent bonuses to Igniting someone with a primarily Fire hit.
The fact that the path of least resistance when creating an Ailment build will usually lead to having base damage matching that of the corresponding Ailment is too obviously a mere correlation, damaging both the fantasy of āplaying by the rulesā and ābreaking the rulesā: for example, the Soulfire Uniqueās ā+(100 to 160)% Chance to Ignite on Hit with Fire Skills and Necrotic Skillsā attribute is probably BiS for some builds due to sheer magnitude of modifiers, but the fact that I could already Ignite with Necrotic hits with no inherent downside by scaling generic Ignite chance damages the fantasy, the flavor of this item. Imagine if, instead of Soulfire granting some conditional Ignite chance, it instead extended some inherent bonus towards Ignites from Fire damage to also be scaled by Necrotic damage? Now that could be both build-defining and highly flavorful.
To illustrate how I imagine Ailments and applying hits/DoTs could be tied more closely together, suppose every infinitely stacking damaging Ailment gained a small bonus based on the Base+Added damage of the applying Skill: something like āfor every point of Base & Added Fire Damage of the applying Skill, Ignites applied by said Skill gain 1% increased Damageā or āFor every point of Base & Added Physical Damage of the applying Skill, Bleed & Poison applied by said skill have 0.1% increased Duration.ā
Another illustration: suppose a core Ailment was changed to buck the trend of āRapid stack applicationā and instead worked like in PoE, where the ailment cannot stack or is only limited to 2-5 stacks, but the ailmentās base damage scales off the matching damage type in the applying hit; admittedly, thatās more an issue of Ailment identity than of the relation between Ailments and their applying hits, but in changing an Ailmentās identity in this way, it would also tie its scaling more closely to the damage type of the hit that applied it.
Finally, consider the idea of maluses: suppose that if a hit that is less than 50% Fire applies an Ignite, then every % of non-Fire damage over 50% causes a corresponding 1% decreased duration. So, a hit that deals 10 Fire and 10 Cold damage would have no malus, a hit that deals 8 Fire and 12 Cold would apply Ignites with a 10% duration debuff, and a hit that deals 20 Cold damage would apply Ignites with a 50% reduced duration; and so on for other Ailments.
All of these numbers & concepts in the last three paragraphs were pulled out my butt and in no way meant to be serious suggestions, merely illustrations of the overall concept I am driving at.