I still see the timing of the decades as way too compressed if you were to take that passage literally. I prefer to view it as generations. GongZi Yu and Fu HongXue were around 37, I believe...
I don't doubt that FHX was the top fighter in that story. And yes, many times the person who wins isn't necessarily the best in terms of raw power or reputation. I agree w. everything you said about the psychological/confidence factor. But for me, A Fei seems to convey a more awe-inspiring gap of power between himself and other top fighters in BCLZ (and they were no slouches), then FHX did in TYMYD. If one accepts that young FHX/YK ~= young A Fei..... well, even Little Li didn't make me feel that he could embarrass a young A Fei/JWM in the same manner.
Granted, FHX pretty much won all his battles easily... but he didn't seem to be THAT invincible (albeit he was the best), it seemed that he was still grounded.... that he still may be mortal, whereas A Fei was almost magical. Just impressions for the most part (although impressions can be very important in judging GL's characters).....
I can't really say there was definite proof, so you won't find me arguing too hard against FHX. His sabre is faster than the speed of thought, after all.