Mainly plot is what keeps superman from beating flash, flash can be beaten by ppl without powers etc etc but one of the most obvious is his weakness to ice , superman can reach absolute zero with his frost breath , ive seen wally get tripped up by a gorrilla slamming his fist into the ground causing an earthquake mes his strike knockin him out lol u can argue for plot for both superman and flash but remove it and only one has access to the others weakness