Prior to the combat changes, the majority of our songs had a cast time of 3 seconds. So, made good sense to have slower weapons, since there was plenty of time for their "swings" to refresh while casting CAs.
Now after the combat changes and cast time of our songs being lowered to 1-2 secs, high delay weapons (like the 2.1 delay leafblades) dont always refresh inbetween CAs, even iwith high haste.
I know that some dirges are able to reach very high haste percentages... and for them, high delay weapons might be the optimal way to go. But if you arent able to get atleast 50% haste, then I dont think that >1.6 delay is worth it. Simply because weapons wont refresh between CAs.
And if the delay cap is indeed 0.8, then the above makes sense with CoB as well. CoB Adept 3 is 45% haste added to the 50%. This would make a 1.6 delay weapon come in just over 0.8 delay. Ofcourse again... if you are able to reach an insane haste percentage prior to CoB, then higher delay would make sense... for instance leafblades with 100% haste + 45% from CoB would get to roughly 0.85 delay.