ARC takes a position (apparently) opposite to that of Jadis. They feel tubes sound better when run fairly hard (up to a point, of course), one reason ARC amps are known to burn through tubes faster than do some other brands.
Music Reference's Roger Modjeski, in his talks at the Burning Amp Festivals, illustrates (with graphs and other data) that an amp will sound "best" (lowest distortion, greatest linearity) when an amplifier circuit uses any given tube in the "sweet spot" of the tube's performance envelope.
For those great Modjeski tutorials on tubes and tube amp design, go to YouTube and do a simple search for Burning Amp Festival. There you will also be able to see equally illuminating talks by Nelson Pass on the subject of solid state amplifier design.