Do Primary slot instruments allow you to use a shield as a Bard?
 

I see that some of the high-end instruments like Drums of the Beast are Primary slot instruments. I know this allows you to use a weapon in the Secondary slot, but can you also use shields?

yes

Awesome! Thank you!

The question is why? Some weapons have AC and IMO a shield is too heavy for a bard vs a weapon.

You generally find better resists on shields, which is more appealing than A/C for raids and what not.

Cause bards best enrage tank

Shield ac (if it works here the same way as it did/does on live) is not subject to any hard or soft caps. No class dependent returns on ac. No penalty at all. 25-35 shield ac is a lot more potent than ac from any other armor slot or weapon.

If you’re going to be taking damage you’ll take less with a shield equipped.

Is this true for weapons that give AC as well or just shields?

Without any testing whatsoever, I believe it is only shields / held off hand items