Prone is absolutely ideal for me when feasible and lots of big game kills happen this way (see poll results).
The sad truth is that for the vast majority of shooters, they look like a monkey trying to hump a football in ANY other position other than prone. So everyone just defaults to this position when it may not be the most ideal.
When we set up on steep faces glassing up or down I’ll ask folks… So if a shooter buck or bull stepped out right down there or up there at 300 yards how would you kill it? They immediately start trying to find a place where they can “clear an area” and get setup for their prone shot. Only to realize that the terrain and vegetation don’t allow for it, or they have to move and try to get a “lane” or “spot” they can “get proned out”. Normally this also leads to them not having a tall enough front rest to make the angle work as well and over half the time the kill opportunity has long passed.
Looking through kill photos in my phone and remembering the shots… Generally, private property cow elk in Wyoming or white tails in Minnesota are the only kills where I personally have had good/quick enough opportunities to take a prone shot. California sierras and foothills have also allowed for a fair amount of prone shot kills on deer.
All other hunts across the other states and countries the vegetation, steep angles, terrain, and lack of an area to get setup for prone shots leads to many more seated or kneeling shots.
I think if more folks practiced shots other than prone they would be more creative and effective killers. Seated as mentioned, can be nearly as stable as prone when practiced. Especially when leaning your back against a rock, tree, hunting partner, and using rests properly to your advantage.