Well then you're just falling victim to the article posted (And dang it's a good read lol) by Aryia. EDP is a SKILL of the SinX, that happens to boost all Katar based skills, unlike Soul Destroyer which is already beefed up, hence it's unaffected by EDP. So you're saying that by playing a Katar SinX all you're doing is limiting yourself on both weapons and skills to defeat said SinX opponent. Not to mention, with dagger's, SinX are able to toss Shield on and still SD, reducing 40% damage from you WHILE armor switching while still outputting damage to your dumbass because you can't do shit w/ a Katar on besides swap shield and stop attacking to minimize the damage of SD. So really you're losing because a choice of gearing, just like most TSS champs would beat Combo champs, or Int Prof would beat a Autocast Prof, or a bow Stalker vs. a dagger Stalker. It's simple matchups... Even I used daggers in those old best 2/3 duels back in the day on SinX.
If you don't think gears help either, I did some fun math on CK overups: Base damage difference between +4 and +8 CK's are:
348-1020 DPS. That's like... 1.5k-5k more damage every 5 seconds of DPS difference. Somewhere around that, which means you have to be THAT much more efficient at armor swapping.