There will always be the mathematically best possible choice for a mundus stone in a PvE environment.
However the problem goes deeper as currently neither shadow nor thief see use in pvp scenarios aswell. This imo points towards them clearly underperforming compared to alternatives as even in niche build scenarios warrior/apprentice will give better overall results.
By removing healing from Shadow, this mundus now definitely deserves to perform (on average) better damage wise even at relatively lower crit chance. Warrior/Apprentice currently buff crit damage, non crit damage, crit heal and non crit heal. Shadow just crit damage.