solidus snake, it seems then, according to you that Flash is the key to victory for the JLA
your description of the FLash makes it seem like he could actually singlehandedly beat the entire Avengers, after all he just needs to do IMP all day (which to everyone else would be less than a second) and have defeated the entire avengers
now while that is theoretically possible, Flash rarely if ever does that, or else why is the justice league even needed? just ask the Flash to do everything in a pico second and he could save everyone
however if we are to talk about what is merely possible, then it is possible that The Scarlet WItch, before the fight starts, creates a magical forcefield around her teammates, thus rendering FLash's attacks utterly useless, maybe she can turn them invisible so the JL can't even see them, etc