I'm posting this thread to try to make sure this feedback on Blood Weapon is visible for the dev team and also hopefully give people a place to post their own feedback as well.
Simply put, Blood Weapon is in desperate need of a rework as its current design has a ton of issues both with the skill itself and how it interacts with DRK's toolkit.
--Issues--
1) Blood Weapon doesn't actually last a full 10 seconds. The buff and tooltip may claim it does but the effect wears off around 9.5 seconds.
- This is a major pain point for Blood Weapon. The fact that the buff from Blood Weapon wears off early makes reliably getting 5 hits in difficult at best for players with lower latency. The timing on this buff is so unforgiving that any amount of delay on hitting your attacks for whatever reason (be it from lag, hesitation on the player's end, or not enough skillspeed) will often wind up with that 5th hit not benefitting from Blood Weapon at all.
2) DRK's toolkit in AoE situations is comprised of mostly spells which lock the GCD in at 2.5 seconds.
- This issue ties somewhat into the points brought up with the first issue. Getting 5 hits under Blood Weapon using DRK's AoE combo is currently impossible due to Unleash and Stalwart Soul locking the GCD in at 2.5 seconds. As it currently stands, you have to purposely prepare yourself for Blood Weapon in AoE situations by reaching 100 blood and prepping Stalwart Soul so you can get 3 spenders off, which are weaponskills, combined with Stalwart and Unleash if you want to get the most out of Blood Weapon in AoE.
Both of these issues tie together to make Blood Weapon just feel needlessly punishing. The MP and Blood gained per GCD action under Blood Weapon point to the design decision that players should aim to get 5 full hits in whenever they use the skill so they can gain 3000 MP and 50 Blood. So, when you fail to get 5 hits in it feels bad which leads to the skill feeling more punishing than rewarding.
Blood Weapon doesn't have to be like this though. If the skill was simply changed to have 5 stacks that were consumed each time the player used a GCD weaponskill or spell with a 15 second duration, the problems that currently plague Blood Weapon would be fixed.