I hate to say it, but I agree with this 100%.
Spock (via the writers) was ridiculous in this episode.
"Shoot to frighten." ???
Showing a bunch of ape-men that you have some kind of 'fire-stick' that misses what it's being shot at. They would have no concept of shoot to frighten. Purposely missing them makes the ape folk think they are weak.
At least blasting one of them with the (already established)heavy stun setting is way better.
while not attempting to use the stun is an oversight of the writers, it might be better to just imagine in your head that they found out the stun setting doesn't work on these creatures, and it was determined off screen. Cop-out, I know, but they could have easily have said that in the episode and we all would have bought it. then everything else is the same
Then shoot to kill, one of them or the remaining 6 of us.--regretable OR
disintegrate some rocks or whatnot to show the primatives what the weapons can do.
Basically you don't impress the enemy by missing.
Starfleet, especially a Vulcan, isn't going to just shoot to kill some unknown intelligent lifeform, especially when you are intruding on their planet (willingly or not)
They could have disintegrated some rocks, but it probably wouldn't have made any difference, really. Would have been a good thing to try, though.