For Greymoor, most progression groups did not see a benefit to using Galenwe as there are much better or consistent sets one can use particularly for progression groups. For groups that min-max, Galenwe did provide a DPS increase (~2 to 3% at absolute most) and did replace Torug's wherever Torug's was used although Torug's itself is seeing much less action due to the arrival of Yolnahkriin, but the uptimes and the damage increase from Galenwe will also varied for fights that you intend to use the set for taking into factors such as mechanics/rate of successful blocking.
Post-Markarth with the changes to how ALL Empower buffs work ALL Light Attacks for three seconds, the Necromancer skill Empowering Grasp will still probably take precedence over equipping an entire five piece set.
To give some actual context on the efficiency of Galenwe pre-Makarth, the last boss of Kyne's Aegis Hard Mode had 29% of light attacks were Empowered for the highest parsing Damage Dealers from the PC/NA guild 4D, which translated into roughly 1.5k dps increase from light attacks, and a less than 2% increase to overall damage.
For that fight, it's slightly subpar compared to Yolnahkriin which provides roughly a 2% damage increase. Basically it will be a highly situational set where you need to consider first if the group can get away with using it over a different set such as Ebon or whatnot then you need to assess if it can grant a good enough uptime.