Hi Greziz, thanks for the build advice!
I don't think that a long dagger build with 9/10 WM and 10 Athletics is necessarily goofy, if the thrusts are aimed at the head, once you factor in the speed bonus to damage. I'm only level 18 now and the main things keeping my k:d down are the facts that close-range attacks bounce off and that it's really hard to throw a thrust instead of a swing in a tight, turning fight. As for not doing any damage with 3 PS, I've been told that, with 6 Athletics and something like 140 WPF, my running stab to the a 40+ armor helmet will take nearly half of someone's health. I've had several two-hit kills from facestabs and a couple of one-hit kills, though of course I can't know how wounded they were.
In any case, it sounds like you don't think the swings are very good too. I don't think the chambers that they enable are very useful either. Is there anyone out there playing a dagger build who credits the chambers or swings with doing much for them? If not, why keep them? Maybe there should be just one high speed, all-thrust, low-range weapon, and maybe the long dagger is right for that.
It would be different if the long dagger's swings had pierce damage instead of cut, though. But there would still be the problem of the swings being a shorter range and "bouncier" than the thrust.
For now, I have much better with the wakizashi and military pick.