[Arran]

Mike, Joseph;
The better TRF designs from the late 1920s and early 1930s are not too bad for selectivity, sensitivity is no issue as they are as good, if not better, then the average superhet. However I have one of the infamous "Plant A" AC/DC sets, and it only has two tuned stages, the sensitivity is fair, but you need the fingers of a safecracker to tune it with it's direct drive dial.
As Mike correctly pointed out, in the early 1930s there were not as many stations, and many were low power compared to today, 15 KW, 10 KW, 5 KW, some were only 500 Watts, 50 KW ones were the exception. I think this is where the notion of adding more and more tubes to sets came into play, more tubes equals more gain, which reached ridiculous levels by the late 1930s. Other then with the audio amp there are only so many extra features you can add to an AM radio before the law of diminishing returns sets in, double conversion, variable IF bandwidth, extra IF amps/stages, extra TRF amplifier stages, AFC (yes some sets had that too). But after the war the power output of AM broadcast stations became higher and higher, such that 50 KW became typical, so nobody needed a 15-20 tube monster unless they were a Ham, plus TV was the big thing.
Regards
Arran