Flashy Flash is overrated

tl;dr I think he's the strongest S-Class behind the top tiers (Blast/Tatsumaki/King/Probably Metal Knight), but I don't think the gap between him and the likes of Atomic Samurai, Bang and Darkshine is nearly as big as some people seem to think.

Probably not a popular opinion, but I really don't get why off-brand Griffith is glazed so much in this community. People saying shit like "his sword swinging speed is faster than Atomic Samurai!", or "he's more durable than Darkshine!", or "his punches are stronger than Bang's!" is just dumb to me. Most of the S-Class are 'the best' at something: Bang is the best martial artist, Tatsumaki is the best esper, Atomic Samurai is the best swordsman, Darkshine has the best durability and physical strength, Metal Knight has the best tech, Pig God is the best at eating, Flashy Flash is the fastest, etc. Yes, Flashy Flash is strong, but he isn't portrayed in the same way the truly busted S-Class like Tatsumaki and Blast are, so having him outperform his peers in their own fields doesn't really work.

"He's more durable than Darkshine"

This one is dumb for several reasons, but I'll get the biggest one out of the way: steel wires. He took damage, albeit superficial, from steel wires pulled by a demon-level monster. "But Gale Wind used Flashy Flash's speed against him!" no, he said he was going to use Flashy Flash's speed against him. Looking at the actual panel of him being hit by the wires, he doesn't seem to be moving that fast. So you're telling me that Darkshine scales below steel wires?

"But Darkshine was knocked out by one punch from Golden Sperm while Flashy Flash took many punches from Platinum Sperm!" By that logic Iaian, Atomic Samurai and Puri-Puri Prisoner are all as durable as Darkshine because they also took hits from Platinum Sperm and survived. All this means is that Platinum Sperm was putting less effort into his punches than Golden Sperm was, and Darkshine just sitting there waiting to be hit probably helped too. Golden Sperm is about 80% as strong as Platinum Sperm (based on cell counts), so him being able to deliver a punch stronger than Platinum Sperm's casual strikes isn't unbelievable.

"His sword swinging speed is faster than Atomic Samurai"

Granted, there's more of an argument to be made here than with the Darkshine one, but there really isn't anything definitely proving this. "But he shocked Atomic Samurai with his speed" No he didn't. I've only seen this point be made a few times, but it honestly annoys me more than most other instances of Femboy Flash being overhyped just because of how much of a blatant misrepresentation it is of what actually happens in the manga (the "shocked reaction" in question), all those little black lines really mean is that Kamikaze noticed something and was, at best, mildly surprised, which makes sense given that he was just facing off against nameless fodder and something much faster than said fodder suddenly appeared. Flashy Flash himself was more shocked by the ninja twins' speed, who were definitely not faster than him. You'd think the world's strongest swordsman would have more to say if he just witnessed someone outperform him in his own field.

"But the constellation feat!" The constellation that Flashy Flash was a part of was around long enough for random people on the ground to notice it, and given the fact that there was no timer, there's really no way to tell just how fast they were going in relation to other speedsters like Atomic Samurai and Bang. And you can't use the Garou/Platinum Sperm constellation as a reference, given that it was clearly a lot faster than the one Flashy Flash was a part of. They covered more distance in a fraction of a second than they did with Flashy Flash during their bout that presumably lasted several seconds, given the fact that bystanders noticed it. Sure, it's possible that Flashy Flash was moving faster here than Atomic Samurai's sword swinging speed, but there isn't any evidence to prove it definitively, much less make claims like "Atomic Samurai can't even perceive Flashy Flash!"

"He punches harder than Bang"

Again, there really isn't anything to support this. His attacks never damaged Platinum Sperm, so there's no way to actually tell how strong his punches are compared to Bang, but realistically, he probably doesn't hit as hard with his fists as Bang.

"Flashy Flash vs Platinum Sperm was competitive"

No it wasn't. He ran away for most of the fight, threw some punches that did nothing, and got folded, all while being mocked and monologued at by his opponent. Nothing about that is even remotely competitive. Yes, his performance was impressive, but let's not pretend like he stood a chance.

"But Platinum Sperm wanted to team up with Garou against him!" Yes, Platinum SPERM did say that. He had spent his entire life, up until literal moments before this point, having an extreme numbers advantage in every fight. It's more likely that this exchange was just a force of habit than anything, and with how easily he bodied Flashy Flash afterwards, he didn't have any reason to be scared. Besides, Black Sperm is a cautious fighter, even against opponents he has an advantage over, so this really doesn't mean much.

"But Platinum Sperm called him the strongest!" Platinum Sperm referring to Flashy Flash as the "level a mere human being can reach" was likely more of a broad statement about S-Class heroes in general, and even if it was specific to Flashy Flash, Platinum Sperm is hardly a reliable source. It's stated that during the Platinum merger, only one of the billions of sperms would actually be in control, so Platinum Sperm was almost certainly a Black Sperm before the transformation, and he really wouldn't have any way to gauge how strong Flashy Flash is compared to the people he fought. Atomic Samurai was too fast for Black Sperm to perceive, and Black Sperm's attacks did nothing to Darkshine, so he'd have no way of knowing just how much stronger they were than him, let alone how strong they are in relation to Flashy Flash.

Conclusion

Flashy Flash is strong because he's a good all-rounder. He has top tier speed, top tier/high tier durability and top tier attack power, but that doesn't mean he's better than Bang/Darkshine/Atomic Samurai at their respective niches. It also just wouldn't make sense from a reading perspective. Darkshine's durability is treated like a milestone, with Garou outright saying that if he can break through Darkshine's defence, he can break through any defence, and with his durability being used to demonstrate the attack potency of Golden Sperm and Vomited Fuhrer Ugly. Atomic Samurai's entire gimmick is that he's the embodiment of the anime/manga swordsman and can instantly slice his opponent a hundred times, so having Flashy Flash be faster than that just feels weird, especially since Flashy Flash's speed doesn't have that same flair and personality as Atomic Samurai's slashes. He doesn't have the pause between his attack and his opponent dying, nor does he have any "you're already dead" moments like Atomic Samurai.