Teeth, the longsword has a length of 106, 1 more point than the longest 1h, and vastly superior overall stats compared to any 1h cut weapon (it's hard to compare it with hammers due to knockdown).
Basically, anyone playing 1h no shield would be
much better off being a longsword (or even better, HBS) user. And that's exactly what I plan to do personally when I get my hands on that respec thing. Going 2h also allows for a much greater variety of roles, as being able to use a longsword without bouncing pretty much means you'll be able to use any 2h effectively, the LS being on the lower end of the damage spectrum unlike viable 1h weapons which are in the higher end of their category. You can switch to any great sword/miaspamocopterdao or even the best crushthrough weapon in the game if you have 21 STR.
Addition to what teeth said, 1h is the best weapon in clusterfucks. Meaning you will have superb hitting power compared to shielders and better animations compared to other melee classes. The place where swashbucklers shine is clusterfucks, therefore mostly siege (and ships).
You won't hit any better than shielders, except if you count the handful of skill points you can spare if you don't put any point in shield skill. As someone without a shield and with low reach, the only way you can deal with multiple opponents is by using your movement speed, either to buy reach, either to put one behind the other. In a real clusterfuck, you'll no doubt have allies around blocking your way which will lead to your death. Also your right swing is useless if you have anybody on your right, which is pretty damn always in clusterfucks. To say that 1h no shield are the best in clusterfucks in pretty much the opposite of the truth. 2h and poles do better because they kill things and shielders do better because they got a shield. The place where this "class" really shines the most is duels.
Of course I'm only discussing pure swash. When you put ranged hybridizing in the equation, 1h no shield is a pretty solid choice.