Who said “ flat freq response “ is the best?

The performance space affects the sound on the way to the recorder. Your room affects the sound that comes to your ears.

Having amplification that has an output that is exactly the same as the input except for variable volume, just gives you the chance to hear something like what you would have experienced at the performance - except for your other gear and your listening room, which is unlikely to be totally passive.

But if you can at least eliminate one source of colouration, I'd view that as a positive move.