Think of WYY as a tennis coach. You can still give pointers to the #1 player even though the #299 player would whup your ar@s on the tennis courts.
In any case, JY did show her limitations. She cannot give advice on martial arts she never read the manual on (e.g. 6MSJ and XZ's arts). And even for basic moves, she cannot do anything when they are executed too fast (e.g. when she tried to comment on XF using basic moves in Apricot Forest).