Not everyone can switch out their mainhand dagger with something else. They have to choose rapidus, triplus or kila offhand because their main hand dagger is fixed.
You make it sounds like a relic is an inconvenience. Personally if I owned Mandau I would go for the tried and true and use Mandau/Rapidus. I know you love your strength kila but rapidus gains tp so fast that more weaponskills is probably better than slightly stronger ones when it already averages 4-5K because of what abyssea is. The str kila +2 isn't a bad choice, but the loss of tp gain may not be worth it. 176 + 150 is blazingly fast, and you can't judge a weapon combo's DoT based solely on the damage/stats because it ignores fSTR (which is often capped inside abyssea). Once you factor fSTR and increased tp gain the Mandau/Kila +2 versus Mandau/Rapidus is not as clear cut as it first appears.
On a somewhat related note I like my Twilight Knife but I can feel the difference in speed from Kila +2/Rapidus versus Kila +2/Twilight, so much that I actually dislike Kila+2/Twilight. I'm going to try out Twilight/Rapidus in the coming week and see what I think about that though. Twilight's base damage is slightly lower than Kila +2 but delay is the same, and it does get 3% quadruple attack. By my own words "weaponskilling more often >>> weaponskilling slightly harder", but it's difficult to weigh kila +2's 3 base D + 9 str/24 ATK against 3% quadruple attack and what does appear to be a 10% activation on tp drain. However since the HP drain is a true DRAIN effect it damages the mob even if the chatlog says I heal 0 hp, making it a DoT boost similar to Sirocco's wind damage (not to meantion it's a constant self cure). I have a feeling I'll pick Twilight/Rapidus after I get a chance to try it out, but only time will tell. Edited, Feb 7th 2011 8:38pm by Melphina
There are 10 kinds of people in the world. Those who understand binary, and those who don't.