This table is from Chainmail, the earliest combat system for Dungeons and Dragons.
I wish to draw your attention to the first three armor class columns: No Armor (9), Shield Only (8), and Leather Only (7).
As you can see, Shield Only is a better defensive option than Leather Only.
Against four weapons, Sheild Only is better than Leather Only. Against the other nine weapons, Shield Only is as good as Leather Only.
Somewhere in translation, Armor Class 7 (Leather Only) mistakenly became better than Armor Class 8 (Shield Only).