What matters imo is primarily the 'keel' of the bike - fork blades, down tube, chainstays. Other stuff can be pretty thin-walled without losing much stiffness.

Since the builder won't tell you where the tubing is coming from, I would assume Taiwan. Is it at least seamless tubing? Not that seamed is bad per se, but we're talking Taiwanese (?) tubing of undisclosed origin/alloy, so if it is least seamless, I'd consider that a plus.