Yes, I agree. I have always practiced off hand a lot. I sight a gun in from the bench, then I practice from then on, mostly off hand, because I believe in practicing like I will probably shoot in the field.
I use a rest when I can, and I envy anyone who can get into a solid sitting position in the field, and I remember seeing pictures of Jack O'Conor in a sitting positon, shooting at long range. But a man has to know his limitations, as Eastwood would say.
And I never could get into a solid sitting position in the field, unless on a steep hill side or something, and Prone is usually not practical, due to brush, etc, not to mention sometimes it's wet and muddy.
I have killed deer at 200yds off hand, on several occasions, but I probably can't do as well now days as I was capable of when younger, because I don't practice as much. But as far as I am concerned Off hand shooting is your most important practice position.