Testing out whether or not having enough faith to 'properly wield' the shields will impact how well you can block, this is mainly going off of (and against) the Dark Souls Wikia where they said Faith doesn't matter for blocking or parrying. But I'd say having half the amount of times you can block, even for the higher stability Sanctus compared to the Target Shield, is pretty bad.
Appears on these pages
The Sanctus is a medium shield in Dark Souls. Sanctus can be found when Paladin Leeroy invades...