As far as I know, there is no reason whatsoever to ever invest more than one skill point in that skill.
The other nodes are fine (RR, stacking DoT), but the main node doesn’t bring anything of value (low, non-stacking damage, debuff of dubious value).
Changing the WD’s attack from a debuff to an actual attack would allow their damage to stack… but would change the RR type to a non-stacking type, so nope.
Adding a 4th minion at slvl 24 as is the case for Guardians and Blade Spirit would sure give an incentive to sometimes invest in the skill, but it would be slvl 1 or slvl 24, with anything in between worthless, so not a good option either.
Increasing duration would be good QoL, but not exactly good value for your skill points.
Adding Fumble on top of Impaired Aim would be borderline OP…
I dunno, but there should be some reason to invest in the skill.
Since any non-savagery Shaman lacks OA, maybe a DA debuff ?