What is this DC in PK? I can't find a good definition other than some reddit posts.
Here some definition from reddit post:
DC of your spells determined 10 + (level of the spell) + (your casting ability score modifier) + various (like spell focus) bonuses.
Level of the spell is 2, what is the "casting ability score modifier" and from what it derives? Spell focus bonuses? You mean focus on school like conjuration? Why the hell this is not in the game explained properly and i have to read some obscure posts on other websites?
Thats why you have trouble, you dont know the ruleset, you need to work more on your party composition. Linzi is a great support character , her song dirge of doom is mandatory as it applies shaken on foes without any save, then you have unique spells like good hope . One reason linzi dont need to be min maxed, she can heal she can support but she wont overcome magic defenses but she wont have to use such spells she will sing, buff up the party ,heal.
You have not specialized enough. When you want a caster you pick one school and focus on it , then again when i say caster in kingmaker its better to be sorc with high CHA (not int!). The wizard is better in pen and paper, in a computer game focused on combat you pick sorc .You pick the feats related to that school if its conjuration, spell focus conjuration, greater focus conjuration . When you cast stinking cloud the foes will have to roll a save the higher the DC the higher they have to roll so even if this random they evenutally be fucked up sooner or later they roll each rounds . Control spells are extremely powerful
Then if you want better summons you pick augment summoning etc...
Now there's save DC but there's also spell resistance, when your foe has spell resistance you need to overcome it, so you roll a D20 and add CL ( caster level ) . So its random yes but if you add the feat spell penetration and greater spell penetration the odds are much more in your favor,its likely the spell will land.
A good caster is feat starved and need those.It's possible to spec octavia that way if you dont want to pay for a merc. Also set the game on challenging and use turned based mode its closer to the rules if not perfect.