I really doubt the Vulcans would arm a bronze age civilization on a developing planet with muskets if they thought the Klingons might also do That.
If anything, I think that it might be more likely for the Vulcans to do such a thing. Don’t forget that they did interfere with human development a bunch, because they could not readily put them into their existing categories, out of concern for what might happen otherwise.
It does not seem unreasonable that under the same circumstances, they might find it logical to arm a bronze-age civilisation against an alien enemy.
If anything, I think that it might be more likely for the Vulcans to do such a thing. Don’t forget that they did interfere with human development a bunch, because they could not readily put them into their existing categories, out of concern for what might happen otherwise.
It does not seem unreasonable that under the same circumstances, they might find it logical to arm a bronze-age civilisation against an alien enemy.