As it currently stands at 40% heal reduction, and the current meta makes it the most useful against tanks that heal a lot, it is almost completely negated by a spirit visage 
which gives 30% increased healing from all sources.
Should this be something that gets looked into?
Yeah Grievous wounds is useless atm.
Yes, a good way is to increase the duration of grevious wound on exec blade and morello up to 5 seconds and make mortal reminder grevious wound percetnage from 40% up to 50%.
SV makes GW 22% instead of 40%. Maintaining over 50% of its effectiveness is far from "almost completely negated".
Dr. Mundo Sadism Total health regenerated increased to 50 / 75 / 100% of maximum health from 40 / 50 / 60%.
This change was nealy entirely due to how easy riot made it to get an early grievous item, if we want stronger grievous wounds then the components need to either be weaker versions or its only present on completed items.
40% may be pathetic especially when compared to the what 70% healing amp from aatrox ult but unless they make different grades of Grievous theres not much to change. Or what seems to solve most problems make melee attacks apply a stronger variant than ranged, it is more riskier doing it from point-blank than 600 miles away as an adc.
