I fly into LCY with 5.5deg glideslope.
To do this, drag has to be used to stop the engines "idling". On the RJ/146 it was the airbrake. On the EMB190 it is the lift spoilers.
So thrust settings are not much less than on a normal approach.
I would not like (or be allowed) to do an idle thrust approach.
Think how long it takes for the engines to spool up on take off.
Imagine on approach with idle thrust as suddenly your airspeed goes from Vref +5 to Vref -5. It will be a very uncomfortable few seconds before you get any help from your engines to regain that speed.