To me, it's not that Parrying is too weak, it's that shields are more or less useless. Shields are a "special case" kind of thing. Ranged and certain monster attacks, that's it.
From a "realistic" POV, shields were used for such a long time, because they are versatile. They can be used to simply close off a whole part of the body for attacks, or they can be used offensively, with shield-bashes and the edges used to control the enemy's weapon.
The simplest way to handle this, would be for shields to provide a bonus on the armor rating, like a helmet. Small shields +2, large shields +4. Carrying a heavy piece of wood and/or metal around should give you something, besides those very special circumstances that may, or may not, come up in a certain adventure.
If I recall correctly parrying with a shield was done with a boon in the beta version, but that was later moved to Shield Block.
One shouldn’t forget that blocking with a shield is much safer than blocking with a weapon, since shields in general have a higher durability, and you don’t risk damaging your weapon in a fight.
I’m not too keen on adding a flat armour bonus, since that would lead to quite a power creep.