BDM
OP asked two simple questions. GA target speed is GD and yes protection is there. But this is usual thread discussion. Off course control of the aircraft is primary whether with automatics or manually. But instead of knowing what the aircraft does if you design a new procedure like disconnecting ATHR or reducing below climb to control speed is not smart flying. Executing a GA with AP on requires knowledge of the procedure and not skill. In Airbus, manual flying is not very demanding but it is also necessary to know it's automatics well because that's the way it is designed. What I asked next is a separate question for you to answer.
Incidently if your GA altitude is high say 5000ft and at ACC ALT of 1500ft you forget to bring thrust levers to CLB can you tell me what will happen?
with THR LVRs in TOGA will the aircraft overspeed?