"The rig sounded fantastic". From what vantage point did it sound fantastic? Was there a PA System involved here? What signal path did the bass player have to the sound person?
I have made the same mistake of thinking a rig sounded really good when it was really the PA System and DI setup from the bass player.
Excellent point, and I'll take it a step further. "The rig" includes all points in the tone chain beginning with the bassist himself, to his strings, to his bass, to his onstage amp rig. And as you and others have correctly pointed out, if that bassist ran direct to the PA, then the OP might not have heard the onstage amp rig at all.
I own some boutique amp gear, but also own some Fender gear, and I am impressed with Fender: my Rumble combos and Rumble 800 head. Tone coloration is minimal with EQ set flat. Even if the OP was hearing nothing but the other bassist's stage rig, it might be "grass is greener" syndrome. But again, non-amp factors matter a lot: bassist, bass, strings, etc.