A good rest IMO is a requirement. I hunt on the ground 100% of the time and finding a suitable rest can be problematic, a bipod or shooting sticks instant solution.
I can understand his viewpoint being I too was taught and learned to shoot off hand. It was how it was done before these aides were common, older dogs take time to learn new tricks
. Have him shoot off yours, he may just change his opinion slightly. I know I rarily shoot off hand anymore, it just gives more more confidence to have a solid hold.