they... brag all day that their Yamaha... is just as good.

As noted above, I own Martins and Gibsons as well as several other quality instruments and will say uneqivocally that my friend Robert's Yamaha sounds as good and plays as well as any of them. On the other hand, I've owned a few Yamahas myself and have not been all that pleased with them so his guitar may be an exceptional example.