Same system on many other aircraft and it works fine.
Cleared = arm..... ALWAYS.
If you cleared to do something with todays modern machines you had better arm the appropriate mode.
Do that and learn to bring the flight mode annunciators into your scan EVERY time you select a mode and you are well on your way to staying ahead of the plane
In this accident the fact that the controller cleared them unexpectedly should have been negated had they armed the approach. Loc would have captured and then their only task would have been to chase the G/S using V speed. George was apparently flying for them so that should not have been overly taxing. The failure to arm was the big hole in the cheese IMO.