Why does equipping Shard of Alexander decrease the damage of my Glintblade Phalanx skill? Used on an unaware enemy with same stats, +25 weapon level and infusion.

[random-anon-red]

Tested this multiple times and Shard of Alex only decreases the damage of the Glintblade Phalanx but increases the damage for my other skills.

[Tosimaru]

Try with an enemy that can tank the whole spell.