That seems like a complicated way to test for hFE
The input impedance of each transistor is hFE/gm.
If fed from a source with no or very low source impedance, then the variations in overall gain would have been rather less significant. But the (unknown) source impedance of the generator added to the 1k2 series resistor has formed an effective potential divider with the hie of the transistor, causing a loading effect with is roughly proportional to hFE.
In theory, the gm of the transistor would have been about 200. So for a hFE of 100, hie will be 500 ohms. But for a hFE of 50, we're talking about 250 ohms.
Given the source voltage of 160mV from 1k2, that's 47mV at the base of a transistor with a hFE of 100, or 28mV for one with a hFE of 50.
At first glance, the gain of the transistor should be 240 (200 times 1.2). 47mV times 240 is 11.3V, and 28mV times 240 is 6.7V. Obviously, there's a bit more to it that just that - not least Zout of your generator - but essentially this shows that while the transconductance of a transistor is not affected by hFE directly (assuming Ic stays the same), the changing input impedance will change the overall voltage gain when there is significant impedance in the base circuit. But this should come as no surprise, of course.
(For brevity, I've ignored other effects here - the above should be treated as "back of the envelope" rather than a rigorous analysis. But if nothing else, 470n at 1kHz is far from a short circuit
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What's more interesting is to consider the impedance that feeds the output pair in a push-pull amplifier. The driver transformer is fed from the collector of the preceding transistor (which usually is a CE amplifier, so has a moderate output impedance). This is obviously reduced by N-squared - what's the typical turns ratio of a driver transformer? Given that, we could have a stab at working out the effect of different hFE in the output pair - that would be interesting
