I believe you’re right on the Vox but wrong about the theory. The original Voxes had no standby switch even with diode rectification, something the Korg reissues have rectified (ouch 😳 ). If a valve, like the GZ34 or EZ81, did the rectifying, then the power valves (the EL84s) don’t get an immediate blast of DC before they’ve warmed up. Diode rectifiers send it straight through, so a standby is a good idea to let the heaters warm up.

HST, my CMI-Marshall has no standby and the Mullard EL34s lasted for donkeys and the Svets put in around 2000 are still there (although the amp was gigged a lot less from then).