Yeah, they don't want to add voice chat because it's more overhead for them to deal with and most players use a 3rd party method already. All I can say about the dungeons is that you need to tell people that you're new and inexperienced and they should help you out/ give you some leeway. Once you have a feel for it, it's not too difficult. If you keep having trouble maybe try leveling a DPS instead. People will not notice your screw ups nearly as much. Being a tank puts you in the spotlight and everyone is watching/ relying on you.