I'm a good enough shot and at 15 yards and under, maybe. And in saying that, I still want to google the anatomy. Any further and there are still too many variables to ensure you hit EXACTLY where needed (might miss heart, hit only one lung, really botch it and hit in upper neck or head, deflect off brisket/ribs, no blood trail, exit through guts, buck fever, elk moves slightly). Problem is, you can't google anatomy in the field with an elk in front of you and adrenaline flowing, and there are more ways to LOSE the elk than to get the elk with that shot. On that alone, it should be viewed a borderline unethical shot.
The frontal shot can be the domain of the hunter who can't fully control their adrenaline or know when to stand down, and who are DESPERATE to not go home empty handed. Not a very good look to aspire to. Does it work when it works, yes, just like all similar shots. Is margin of error much more slim than broadside/ quartering away? Absolutely.
With a rifle, I would be more permissive, as it is viable to a longer range and you are relying on the bullet doing some internal work too, and the higher neck shot is also fatal in a way it would not quickly be with an arrow. Muzzleloader I would treat as with a bow, but to a little longer yardage, no more than 50 yards, if well sighted.
Finally - full disclosure - I killed a whitetail with a muzzleloader at 5 yards or less this way and an XTP mag bullet (pretty devastating) and a cow elk with a conical (full penetration and exit out HQ), not the best blood trail. Ran maybe 50 yards. Still wish I had waited for broadside on that - I fit the "desperate to not go home empty handed" noted above and in hindsight not super proud of it, even though it worked.
