If 5lb, give or take, is a widely accepted standard in a defensive pistol... What makes a rifle different? Nothing... Both are susceptible to the same errors.
What makes a rifle different?? The stock, perhaps, and the way it's held?
Now, if you are shouldering an AR pistol, probably not a lot of difference, but if you AREN'T??? what then?
Go too light and you have an unreliable inadvertent machine gun. (aka bump fire)
Anyone who actually knows how to use a trigger can tell you that the actual weight in pounds & oz of the pull is LESS important to accuracy than the smoothness, and crispness of the pull.
5lbs of smooth pull with the desired "glass rod" break is more accurate than 3lbs of mush.