For some reason, people always seem to think "oh, get what's comfortable and fits right".
They then tend to spread this "common sense" around.
The problem is, in shooting what is comfortable is not always fast, accurate or both.
Here's one example. When I was in the Marines I did a lot of MOUT/ CQB training. At the time, the position was almost an old school FBI crouch. It was not comfortable, and would kill your back. BUT, it provided a MASSIVELY stable position to move and shoot with.
Same with hand guns. My big EAA Witness has two grip positions. Comfortable and natural, or accurate. Grab it the natural way, and everyone shoots low and left. Grasp it with the strong hand rotated around the grip just a hair, into a very UN natural feeling position, and it shoots like a damn laser beam kicking out under 2" groups at 25 yards.
A third example is my Olympic small bore rifle, and by extension the traditional offhand position.
ABSURDLY uncomfortable, and literally horrible for your back, but lets you maintain very accurate shots. In the case of smallbore, shooting rounds through the same hole, and high power, fist size groups rapid fire at 200 yards.
So basically it boils down to find out what works.