FRENCH POLISH IS THE FIRST CHOICE FINISH FOR A CONCERT GUITAR
Definitely a myth. Finishing in general is a very complex issue. The term french polish is often misused, which adds to confusion. Extensive testing at Robert Guitars have revealed a very short list of advantages and a long list of disadvantages associated with the use of shellac, main ingredient of traditional French Polish.
SYNTHETIC LACQUER MAKES FOR A BRIGHT, BRITTLE SOUND
Not true. A generalization, has some relevance to poorly applied nitrocellulose lacquer which is brittle.
SOFT FINISH SCRATCHES EASILY
Not true. Try scratching a rubber car tire.
HARD FINISH MAKES FOR BRIGHT SOUND
Not true, polyurethane doesnt.