TCAS (first) gives a Traffic warning and (in a second stage and if the risk continues) shows the pilot what avoiding action to undertake, but it is up to the pilot to disconnect the A/P and to hand fly the maneuver.
The idea of Airbus is to take the pilot out and to let the A/P fly the avoiding action for a more rapid and preciser action.
Studies have shown it takes pilots several seconds (especially in cruise) to respond to an Resolution Advisory from TCAS and also that they often overreact to RAs. 'Reduce vertical descent' does not mean 'stop descending all together' as in dense airspace (e.g. in holdings) this might trigger a second TCAS warning with another plane.
Way to go, Airbus!