Mr. Magniloquent
Arcane
For the price of one character you get a damn near full wizard that can DC cast just fine. The best blaster. Boss slayer. A skill monkey. Scout. Party face. You can even back-up heal in a pinch via UMD and cleric scrolls wands. Kingmaker throws so many consumables at you that you'll get great mileage out of that UMD. One of my biggest heartbreaks about Kingmaker is that you can't get 10 levels of Scroll Savant and 10 Levels of AT. I know it would be a bit of a pointlessly late bloomer, but still. Build-porn. The few weaknesses the prestige class has can be overcome by selecting the option to have the skill check user take all the XP. Spell Specialization comes to the rescue for your clutch spell(s), and it upgrades with you the whole way. This class is my beloved. The only one that has ever come close to it for me is the Shadow Adept from 3.5E.
Except you don't have the spell slots to carry that character unless you take another full arcane caster to cover buffs. And if you do that then you have to compare it to martial builds who do this much better.
Seriously, if you want consistent damage for trash fights, take Sylvan sorcerer. The pet will contribute far more with zero spell slot investment than your sneak attack dice ever would, never even mind the lost level of spellcasting.
You have confused me. AT is only 1 spell level behind, which means you are only 1-2 casts per day fewer. Arcane Tricksters are not for buffing others and spells are never for trash mobs in a vancian system. Spells are for tide turning. Especially in a game like KM whose focus on attrition plays to every weakness the wizard has. That's why mixing in rogue skills is so wonderful for it. They redeems that member slot from being a carry with questionable return. The sea of consumables lets them operate on more than just cantrips or failing with a ranged weapon. This is one more way in which the sneak attack helps you get more mileage on low level scrolls, especially if you're using Scroll Savant. Scroll Savant is a hard trade though. It's a bit of a gamble or an expense, and those fewer feats really hurt. It's a tremendous help and QoL improvement for wizards in Kingmaker though.