So if I understand this correctly, defiling allows the casting of a spell at +1 caster level, but renders large swaths of land barren. While preserving currently has no impact to the land or the caster, is that about right?

What if the preserver was granted some simple boon by nature during the act of preserving, wind whips around the character gently, carrying leaves, sand, or other light debris, granting the character either a deflection bonus to ac, or perhaps minor cover, which could either add to the the casters ac a number equal to either the level of the spell, or another arbitrary number, of if using minor cover it could be the same number, but as a penalty to an enemies attack roll.

This would make defiling a more offensive tactic, wherein the caster is trying to pump out more damage by draining the land. Preserving would therefore be more defensive, gaining protection from the land itself as thanks for not destroying it. This would also make preservers more adept at casting in melee as they would get the defensive buff which could help prevent the dreaded attack of opportunity from hitting.

Just my two cents. Do with it what you will. If I am misunderstanding the mechanic behind defiling and am completely wrong then feel free to ignore my suggestion all together.

Is that Providing offensive spellcasters the easy ability to 'screw nature' and increase the raw damage their spells do (spell level doesnt affect spell DC in 5e anymore); is infinitely more powerful and likely common than those few who want to 'preserve' life.

If we're going to balance the scales, Preserving should be harder (there's less preservable land) but stronger in the outcome. (not sure how yet but will edit when I have more time)

Or. allow preserving to have a immediate impact. (like the land becomes fertile again in a small radius) and when on 'preserved land or land lush with life still' they then get to cast spells at the higher level etc. if the balance isnt there it's noticable why the game world is fubared. it's just too easy to wrack power from nothing lol.

just a thought.

I'll have to look at these answers in depth later. I'm exhausted and I'm going to go to bed.

First post might be a bit late. I'm going to have a busy day tomorrow.