On both Earth-1 and Earth-2, nearly all metahumans got their powers from a particle accelerator explosion at STAR Labs. (There were a few exceptions like Deathbolt, Trajectory, Vandal Savage and the Hawks, and possibly the Earth-3 Flash, but for the most part, metahumans didn't exist before the dark matter wave hit Central City.)
Yet it's doubtful that there was any particle accelerator explosion in the Flashpoint universe. Wally doesn't mention it when describing how he became the Flash, and no one at STAR Labs mentions it. The fact that STAR Labs is still a successful company with dozens of employees would also suggest that the explosion never happened (although that was also the case on Earth-2, strangely enough). So where did all the metahumans come from? They already gave an explanation for Wally, but how did the Rival and Magenta and all the other people Alchemy is re-powering originally get their powers?
Also, shouldn't the timeline where Eobard Thawne was stopped from killing Nora have been nearly identical to the original timeline, where the particle accelerator exploded in 2020? Yet it seems like the Flashpoint timeline is very different from the original timeline: In the original timeline, Harrison Wells still owned STAR Labs, rather than Cisco, and Barry still ended up becoming the Flash, rather than Wally. So what exactly happened here?