The Airbus autothrust is often accused of being lazy, but Airbus fly a constant groundspeed on approach, (incorporating 'ground speed mini'[mum]), not a constant airspeed, so it may dip below bug or reduce the engines to idle, but the groundspeed is still fine. (I realise this is technically not a "stable" approach in the usual definition of the word).
The bug moves with GS mini calculations in managed speed so if the speed is not on the bug the thrust will be adjusting to maintain the magenta bug. GS mini is not hidden from the pilot with the autothrust adjusting to maintain some unknown value, GS mini is displayed via the magenta bug and that is the autothrust target.
Personally I thing the A/THR does a good job, with Vapp just above Vls sometimes it lets the speed decay a bit but I have never seen it go below Vls and there are very quick and large changes to prevent this. Vls is its bottom limit and it does a very good job at not busting that limit.