Compared to Arcane Needle, Withering blade is awful. It's got a 9 second longer cooldown, holds 1 less charge, deals about 30% less damage, has weaker tracking, less range, and has a worse status effect since slow has been so heavy nerfed not to mention unravel adds DOT that can kill as well as spread and spawn tangles. So I feel like it should get some sort of buff to bring it up to Arcane Needles level. Maybe increase the initial hit damage to 75, reduce cooldown by 10-20 seconds, and increase slow stacks to 50. Maybe also buff the travel speed or tracking strength slightly.