1. they are 1 hit kills but you can never hit them like in cod
-which means they suck.
2. they can be super easy to use, but not 1 hit kill
-you would just get sprayed and killed by anyone with a gun
-which means they would suck.
3. they can be super easy to use, fast and impossible to dodge, have a long range, and be a 1 hit kill.
-be overpowered
-be the new awp, but the awp would still be better. so they still suck.
I just don't see any balancing point in a melee weapon being thrown. The only feasable way for it to be any good is for it to be a 1 hit kill while requiring some semblance of skill to use correctly, but at that point, anyone will use the fancier awp. It doesn't have a niche to fill.
1 hit kill weapons have no niche to fill that isn't filled by the awp without being grossly overpowered. The only way a single shot, slow reload weapon can even begin to be balanced though, is if it were a 1 hit kill. Theres just no reason to use it in a tactical sense.