If your form is good (the bow fits correctly) and you aren't fat or super muscular, you should be able to shoot without an armguard.
I only wear one when I have long sleeves on.
Of course, the proper stance (what they call "more open") will angle the arm for more string clearance. That means angle on the shoulder.......so will work the muscles differently (take slight getting used to). Also...............it shortens your draw a bit.
Most folks that hit their arm have a too long drawlength on their bow, and or take a deep grip.
Some people have weird elbow bends.............they're gonna get blasted no matter what.
Open grip shooting is just asking for trouble IMHO. Too easy to develop a tendency to want to grab it.
Many who don't grab it, do a partial grab at the shot. Pretty funny.
Like another stated, touch the index finger to the thumb and curl the others in along side the grip. Bow should be more to the thumb pad side, not dead center in the V of the hand.
Some bow grips suck. The old Mathews factory standard would make hands slide up. They said it wasn't a problem LOL, but most everybody that shot well went with an aftermarket grip (one called the Torqueless). Much more consistent hand placement, repeatability. Later Mathews changed their grip to be more similar to the aftermarket one. Funny.
Watch the really good shooters. They all look pretty much the same...........there's madness in their antics I tell ya