High tends to be treated as a "good" feature but you can get buffs as "high" evil too. But if you build a faction around this you should be able to start with a -10 evil alignment instead of a +10 good one. And maybe change up the unit descriptions and language for now, with more differentiated lore and units later?
#Would like to see a more differentiated "high" evil option
brave thorn
vague hawk
Think of it like this. Every culture has pros and cons when it comes to pursuing some strategy. If you want to become evil you could go dark for a headstart at the cost of other things. If you go high the extra good alignment might slow you down, but you get an absolutely killer unit roster and the awaken trait. It's meant to be a package.
Becoming evil is also way easier than becoming good. Just declare war on every free city you meet and raze their provinces which they never defend. Getting evil is fast and even profitable while becoming good costs you resources and takes a long time
uncut gulch
Not to mention that High’s evil bonus is significantly stronger than their good bonus