All right, I got you. There are a couple things though. -First of all, Kid Boomerang isn't a speedster. Not like Jay Garrick, Johnny Quick, Wally West, Barry Allen, Bart Allen, Max Mercury or any character that can run fast that has or has not appeared in Flash Rebirth. -Has, as far as I know, no established connection to the Speed Force. It's not certain that Mercer is tapping it to throw boomerangs - likely considering his heritage, but not a given. -Lastly, if Prof Thawne ever said "I'm going after all the speedsters" I must have missed that. I can't remember him saying that.