Seriously...
They hit instantly (before their swing animation goes off)
The travel far (i capped vids of them killing me 3 sword lengths away, as well as in my own base)
They travel faster then striker dash (even if you do manage to get away, you wasted a whole striker bar on dodging one combo, and all they have to do is have auto-aim on and click away)
One of the reasons I personally don't participate in Guild Lockdown is because the one time I did, the entire enemy team had rapiers. They dashed around the map and just chewed us up - made me want to puke when one of them ran on the screen and killed me before a bullet left my gun.
Excuse me while I rant a bit... I just watched 3 separate rapier users do 15k+ dmg per lockdown match when most people on the other team could easily out play them... they just didn't have the option to click real fast and get a kill.
Don't get me wrong, there are ways around any exploit in any game. The tier level on that sword in lockdown is just huge though...
If players of equal skill go up against each other, the one with the rapier will generally win.
and take a flourish into the clockworks, and any other 3 swing sword - FLOURISH LINE DEALS THE LEAST DAMAGE OF ALL 3 HIT SWORDS
it is supposedly faster, but not by much and attacks in a very different manor, which can get you killed if your not careful (those spikes can come at you really fast)
Also note that up till strata 6, ie the last 5 depths of the clockworks, an acheron deals more damage to beasts then a fearless rigadoon (now i know that the rigadoon sacrifices a small amount of damage for stun but its a pure piercing sword, you would expect it to be better than a neutral damage sword)
your initial argument has nothing to do with the sword itself, what you have described is lag, something which i play with all the time, as do many others.
in lockdown i have been killed 5 tiles away from somebody using a granfasut - and even they do not have that range
the 'hit instantly' is once again because the server has already determined that you've been hit before your computer is displaying the animation, your location and the others will also differ on the server compared to what you can see which explains why the appear to have an extraordinary range - also the first swing of flourish line weapons is faster and hits a larger area than any other 3 hit sword
also it does require some skill to handle a flourish weapon, especially in LD - possibly more than heavy swords as they tend to kill as long as the first strike hits (at least from what i've seen)
ignore pvp, and most people do, and the flourish could possibly use a slight buff (but not by much), inside pvp wear piercing armour, at least all flourish line weapons deal pierce unlike all other types of swords