GMs
have seen this thread. I even posted in it earlier, about the actual scarf stats.
As many have said, the suggestion has come up before, and we have said "no".
We don't like playing with actual class mechanics, and if we did, it would be to make something even more unique, rather than pushing them directly towards another class (In this case, the hunter classes).
Also, if we tried to push all classes to "the most useful they can be", we'd have ... 1 class. It'd heal, have massive DPS, elements, etc all rolled in to one.
Every class is intended to have their upsides and their restrictions.
Gunslingers have awesome range, great spamability in a high DPS skill, and the possibility of many weapon builds (though, more actual viable ones if Gravity remembered they existed).
Gunslingers are an extended class; They're not supposed to be able to stand on par with Snipers, or any other trans class.
Black scarves help increase damage and survivability enough as it is. Plenty of people in this thread have called them "OP".