So let's do some physics...
Power = Energy / Time
But Energy = Force * Distance
So Power = Force * Distance / Time, which is just Power = Thrust * Speed, with thrust being pretty constant regardless of speed. Easy
So yes, if Speed = 0, the power that's useful for propelling the aircraft
is equal to zero, which usually is what counts.
Of course the mechanical power of the engine is far from being null, which you can easily find out by doing a little walk behind that A380. If all you got it for was to have the biggest fan of the neighbourhood, then it's pretty powerful for one indeed, with power being more along the lines of displaced air mass * air speed difference between input and output.
So, useful engine power, or more importantly efficiency is proportional to speed, which is why you'd better fly fast when you use a jet engine.