The thing with standard AR triggers is they have no travel adjustment screw, something a lot of bolt gun makers went to decades ago because the public thinks it needs a slick light target trigger. In reality, it's just a feel good item - about dead last in priority to actually improve accuracy.
6 pound field triggers work fine with the travel adjusted correctly. It removes 80% of the creep - and 80% of the grit, too, because it simply doesn't reset back behind it where it has to scrape across it again.
Most of the $200+ triggers have those screws, they do have very nice crisp breaks from precise square polishing, and they are nearly impossible to record a specific MOA improvement. It's usually so small the natural inaccuracy of a factory barrel and shelf bought ammo covers it up. Correct handling, and handloaded ammo will do far more for the same money. A turret press reloading kit will get you ammo better than 1MOA, the trigger, not even that and the ammo is required to see it.
Spring kits for the standard AR reduce the hammer power, nature of the beast. Some are known to be too weak for military primers - forcing the economical shooter to start reloading so he can afford the softer civilian ones without paying $1 a round for shelf ammo.
After all, we're talking a combat weapon design, meant to keep soldiers from jacking it up and making work for the armorer. Drop in designs rework the geometry and compensate for things. They aren't cheap, tho, and on a $1 per .1 MOA improvement, rank pretty far down the list.