Do single output device per phase amplifiers like GamuT and Gato have technical merit

Averaging of transistor characteristics, might be one reason, but it also might be easier to find better performing transistors at the lower power ratings.  Practical reasons, like distributing heat evenly on the heatsink as well as easy mounting directly on PCB might influence design as well.   Bad amplifiers can be designed in either scheme.

This is all about distortion and not really about anything else; the argument being that single devices wwon't make as much distortion since there aren't multiple devices where some can hog current (and thus saturate more easily).

Multiple devices allow for an averaging of the device specs- hfe, bandwidth and so on and current limiting resistors can be used to prevent current hogging; and in this regard if complementary devices are used in the output section then its more likely that the composite sum of them will be a more correct complement than you could achieve with a single unit.

But distortion is the overarching issue and to that end with most solid state amps its all about feedback rather than how the output section is designed. In that regard, most amps in general simply don't have enough, so the application of the feedback itself results in distortion while otherwise suppressing the innate distortion of the circuit. Since the added distortion is higher ordered harmonics and intermodulations (occurring at the feedback node) the result is harshness and brightness.


Most amplifiers simply don't have the Gain Bandwidth Product to get around this problem by adding enough feedback to really do the job correctly. And if you are thinking- 'if this is true then no amplifier made has ever been right' you would be correct.


So the result is that the number of devices in the output section isn't going to amount to a hill of beans until the problem I just described is solved. Its precisely this problem which is why tubes are still around as they tend to have less troubles with higher ordered harmonic distortion than solid state and so sound smoother.