Shields are just enough right now in terms of strength. Thing is, shields should be durable, they should be able to shield and protect you from arrows and blows, and more than just 2-4 hits - why? Because otherwise why do we even bother having shields in a Medieval game?
If you believe they are overpowered, let me tell you first that a person that keeps holding his shield up, is also basically a lame mule on the battlefield. He/she cannot move very well, and cannot hit anyone, save for a risky shieldbash for some measly damage. You call that OP? Someone holding a shield for one or two minutes? No, it has functionality and place.
If someone is holding up their shield that allows your team to do so much more. Adapt and overcome. Leave shields where they are right now or even make 'em a bit beefier.
This. People who want weaker shields are basically asking for a higher solo kill count and don't really want a team game. That is fine to want and there will eventually be servers that ban shields but definitely should not be the default M&B which is SP based but for MP is team-based.