The OP mentioned shooting offhand. AR's are a poor choice for shooting offhand. They have zero drop at the heel which either forces putting only the toe on the shoulder or leaning far forward and down. Most of them also have a short length of pull and a pistol grip. An rifle better suited to offhand shooting will be opposite in all these respects. It will have significant drop at the heel, a longer length of pull, and a straight or shallow angle in the grip. The only guns I know of that are currently produced with these features are replicas or reproductions of 19th century lever actions. But M1 Garand, M1 carbine, M1A, M14, Mauser 98, and AK47's with the traditional furniture are all 20th century service rifles with good characteristics for offhand shooting. Show me a single example of a more modern production rifle of any action type that has any drop at the heel and a shallow angle grip. That will be your offhand shooting rifle.
Now it should be noted why we see virtually all straight stocks. The AR's stock is straight because it contains the buffer tube. But most rifle's stocks are straight to compromise for two factors: prone shooting and optics. If we were to look back at offhand match shooting rifles we would see a lot of drop at the heel, more than three inches and those rifles would be miserable in any prone position. Consider the difference in height between the eye and shoulder when standing to shoot offhand versus the difference between eye and shoulder when prone. An old wood-stocked 20th century service rifle finds a compromise with perhaps just a couple of inches of drop at the heel. But after you also factor in the need for a higher comb to use optics, we see late 20th century and present century rifles stocks all totally straight or perhaps with half an inch of drop at the most. It's a compromise that does not work well for shooting offhand but works acceptably for the type of prone and benchrest shooting that's favored by present-day riflemen that are obsessed with 0.3MOA, VLD, ELD, and will buy gear based on 1000 yard performance claims even for their deer rifles.
Now it should be noted why we see virtually all straight stocks. The AR's stock is straight because it contains the buffer tube. But most rifle's stocks are straight to compromise for two factors: prone shooting and optics. If we were to look back at offhand match shooting rifles we would see a lot of drop at the heel, more than three inches and those rifles would be miserable in any prone position. Consider the difference in height between the eye and shoulder when standing to shoot offhand versus the difference between eye and shoulder when prone. An old wood-stocked 20th century service rifle finds a compromise with perhaps just a couple of inches of drop at the heel. But after you also factor in the need for a higher comb to use optics, we see late 20th century and present century rifles stocks all totally straight or perhaps with half an inch of drop at the most. It's a compromise that does not work well for shooting offhand but works acceptably for the type of prone and benchrest shooting that's favored by present-day riflemen that are obsessed with 0.3MOA, VLD, ELD, and will buy gear based on 1000 yard performance claims even for their deer rifles.