You make some very valid points, even for myself. I rarely shoot anything other than bench or prone. Next time I go to the range with or without him, im going to place myself in some field positions and see what kind of groups I get. That being said, I usually hunt from the ground, so prone shots or tripod is what im using. That being said, my father is much like yours. Once-a-year deer hunter who hunts in heavily wooded areas. He also uses a 270 win and he has been doing fine. Maybe ill see if I can interest him in letting me take the rifle and develop a load for it, or just see if everything is in working order. Might not be him at all and just the rifle.
I range shoot all year around plus hunt varmints in the spring / summer, predators in the winter. I hunted deer for about 50 years but due to physical decline, I can no longer hunt them - double hernia surgery kill the ability for me dragging a deer out.
It wasn't long before I realized I needed some kind of field shooting aid, especially for varmints / predators. After trying a variety of field shooting aids, about 25 years ago I began using homemade cross sticks.
To enhance effectiveness, I began using a small, lightweight, portable hunter sportsman's chair. This gave me a stable platform, two feet flat on the ground, elbows resting on the knees. In addition, the increased elevation gave me a much wider field of view significantly increasing my shot opportunities.
While it took some time to become proficient with them, I finally mastered them. After missing a buck of a lifetime in Potter County PA about 20 years ago trying to take the shot by resting the rifle against a tree, I started using the cross sticks to hunt deer like I hunt varmints and predators. I never missed a deer after that.
Almost all my range time is spent shooting off the sticks to simulate hunting conditions. The only time I use the bench is for load development, initial scope sight in, or trying to sort out a problem. I enjoy practical shooting.
With the sticks I can hunt any terrain, deploy them in a manner of seconds, and I have a much wider field of view than shooting prone off a bipod. Ron Spomer, a TV hunting personality, uses them extensively to hunt deer. If you go on his web site there is video illustrating their use. He also has made several hunting videos using them that use to be on the Outdoor Channel.