The topic, “Do more expensive amps/gear sound better than cheaper gear?” didn’t exist a few decades back because we had a proliferation of Brick and Mortar Audio Stores. One could walk in and hear a dozen combinations of amps, preamps, speakers, turntables and CD players and then decide for themselves what sounded best to their ears. And if the sales person sensed you were close to buying they might escort you into their high end hifi room hoping they were not tugging on the line too hard to rip the hook out of your mouth.
These days the brick and mortar stores are more difficult to find and people prefer to shop online. My son, for example avoids shopping at the grocery store. He orders nearly everything online. So it is easier to believe that all electronics sound basically the same and with little to no listening experience of a good hifi rig, they just order that SMSL amp from Amazon.