As I see it
You are quite correct,the thrust levers are only connected by wires to the FADECS and hence the engines, however, the FADECS are self powered as long as the engines are turning.
So the question is, can you control your engines when ALL electrical power is lost? ( that is no engine/APU generators no emergency generator and the poor old batteries are flat)
Do the FADECS supply the thrust lever quadrant to allow the thrust lever position to be monitored?