I am planning a 5e Dark Sun game, and I wanted to use the following rules for homebrewed preserving and defiling.
When a defiler casts a spell of level 1 or higher, each other living being within (spell-level) squares of the caster takes the following necrotic defiling damage:
Spell-Level Defiling damage 1 1 2 1d2 3 1d4 4 1d6 5 1d8 6 1d10 7 1d12 8 2d6 9 2d8
When no living creatures are within defiling range, the defiler takes 5 × (spell-level) damage.
When 5 or more living creatures take defiling damage, the attack roll or spell DC is increased by 1d2.
The defiler rules should make defilers hated, and provide a mechanical base for some of Kalak's actions in the fiction. The high HP of 5e characters and the low number of spell slots make me think that the higher damage for high-level spells is appropriate.
A preserver can choose to use his bonus action, action, or his whole move to focus his magic and avoid damage to the environment. This improves the attack roll or save DC by 1.
The preserver always gets a +1 so that the preserver path is not simply mechanically worse than defiling, but it comes at a cost.
I am aware that it generally raises the attack rolls/DC by 1, this is offset by tactical rules that gives a similar boost to weapon attacks, so martials are not disadvantaged. Therefore, I am mainly interested in balance between the two rules, or comparisons that assume a general +1 for martials as well.
A good answer would show how my suggested homebrew rules are mechanically imbalanced and maybe offer a suggestion how I can keep the basic idea, but with more balanced mechanics.