No doubt the usual issue trigger kit isn't so hot. I've had decent ones attached to issue rifles, but the LPK's coming out in kits or rack grade guns aren't that good.
One specific trait many of the better triggers have is an adjustable reset screw, to shorten up the amount of creep. Most precision bolt guns have had them for decades, and they've become standard on hunting rifles, too.
Since they reduce reset about 80% when properly adjusted, they don't have the creep, either, and that means a lot of the grit is eliminated, too. It's just the last 20% of travel that counts, then. My AGP lower came with it already installed, the before and after are night and day. Short reset, a nubbin of creep, and all but one trickle of grit left. Much improved for a hunting AR.
The triggers on AR's are designed for military use and to keep soldiers from tinkering with them, so the hammer spring loads the trigger weight. Reducing it reduces hammer power, target triggers under 2.5 pounds have problems with hard military primers. Some of the aftermarket triggers change up the pivots and spring leverage to make them different and can reduce trigger weight without affecting hammer power much.
There's also a difference in target and tactical, now, plus the awareness you can have a great trigger and it's still 4.5 pounds - or more. A light trigger isn't necessarily best in the field or on duty - military standards set it at 6-8 pounds for some good reasons.
The best bang for the buck isn't an expensive $250 trigger, you'll get your money's worth, but for the few dollars spent on a trigger adjustment screw, you get 80% of what they deliver anyway. It's the last few percent that are exponentially expensive.