A shitty yet terrifying weapon. Got it.
It is terrifying for factors unrelated to the weapon, but more the nature of the training of soldiers (or lack thereof) and their willingness to kill or risk death.
There is a psychological barrier to killing. It is easier to breach with mechanical and physical distance, pure rage, cultural or class hatred, obscured faces, and distributed responsibility. You can get a few hundred guys together in a line to shoot at another line of dudes, but only a few percent are actually shooting to kill. Most ended up either dry-firing their weapons, loading their weapons eight times and not firing, or firing over their enemies heads. When the bayonets come out, the soldiers break.
Most of the actual casualties post gunpowder have been from artillery and other crew-served weapons.
In the ancient and medieval world, things were a bit different because there were massive amounts of ethnic, class, and religious hatred, and faces were often obscured (so you dont take as much pity on the dude begging for his life, or obviously terrified).
Hell, in WWII, only 2% of infantry in combat (as in, front line, not logistics dudes) actually shot to kill when in a position to do so.
Those numbers are WAY up now because we figured out how to train soldiers to defeat that psychological barrier. But that is the context when bayonets were actually in use.
What they were effective at as actual weapons was stopping cavalry charges because horses wont suicide into a block of pointy sticks.
Also, there is the martial art of Jukendo, or Japanese bayonet fighting, so a skilled Force sensitive could be a threat with one. Remember the United States Marine Corps Martial Arts motto: "One mind, any weapon". Even a shitty one if you have no other option. Also, the lightbayonet could be easily well balanced if made right, and its reach would actually be the entire weapon, since the integrity field would protect it from lightsaber strikes, so you could block or strike from either end as I said before.
You are still holding something shorter than a quarter staff in two hands. That means the reach is inferior to an actual sword. It is also heavy. After the hilt, lightsabers are either massless or effectively massless. A lightbayonet would not be, and as a result will be MUCH slower to use.
Lastly, why the fuck would I carry a shitty heavy weapon when I have the option of a good weapon that weighs at most a few hundred grams?
BTW, I'm not trying to come across as a smartass, since I have to admit I have no military experience. If you do I'll gladly take any correction from you on this matter.
Knife has. I have used actual melee weapons.