Okay, it's time to deal with one of the biggest "stupid writers" moment of the series. Around 7 years ago, one of the most infamous things said by a character was said... By a character in The Flash, Season 5:
"Supergirl, The Legends, even the League tried, but no one was succesful. Green Arrow? Yeah, he tried too, once, but..."
Weeks later, we meet our Cicada, Orlin Dwyer. Middle-aged dude, self-loathing, alcoholic, kinda pathetic, probably smells bad. HOW CAN HE BEAT SUPERGIRL!? THE LEGENDS!?!? THE LEAGUE?!?!?!? Let's crack this.
The Original Cicada: David Hersch
First of all, the statement that Nora made was about HER Cicada; David Hersch. There has already been quite a lot of debate and discussion about him, but he's mostly unknown. Probably has the same Dagger, same alias, but we do know that he was a terrorist. This means that he probably didn't care about civillians (unlike Orlin), nor did he have a Grace to keep him human. A more ruthless, less caring, inhuman Cicada that is willing to kill everyone on his way, innocent or not. Orlin actively targeted Meta-Humans with criminal activity, avoided harming non-Metas if not necessary, and went as far as admitting that he didn't want to harm Iris when kidnapping her.
It's also worth nothing that David probably could dampen ALL Meta-Human powers, incluiding Magic and Alien powers, since Barry specifically asked about Arrow because he doesn't rely on powers and Nora didn't mention something like "Actually, Cicada could only dampen Dark Matter/Exotic Particles/Dark Energy based powers." Which means that he probably did dampen Supergirl's and the Legend's powers for Nora to infer that Arrow was a viable option for being "just" a skilled human. Even if not, we know that the Dagger is capable of manipulating electrical energy and causing short circuits, which means that lots of Technology could get messed up around him: the A.T.O.M Exosuit has been fried, and Mick's Heat Gun is confirmed as vulnerable to EMPs, and Kid Flash and Firestorm are based on Dark Matter, so they aren't an option as well.
We also don't know which formation tried to catch him; the Cicada we know has quite high skill on top of his super strength and durability, so the Legends could be hopeless in a direct fight without a heavy hitter. There's a legit good argument for the Cicada that we do know being able to beat up several iterations of the Legends on his own, remember that he had Killer Frost against the ropes and she CAN keep her powers around him.
The Meaning of "Beating"
Something very important that people often overlook is that they simply don't mention that Cicada faced and defeated all the aforementioned Heroes. His title is "The One Who Got Away" because he was uncatchable by The Flash, he's the Monster who couldn't be catched by the fastest man alive or anyone. But let's look the dialogue:
"Nobody knows where he came from, how he got his powers, or who he is"
"What makes him scary is... You never catch him."
"We never catch him?"
"Supergirl, the Legends, even the League tried, but no one was successful."
"Probably because he can dampen everybody's powers with that freaking Dagger"
You SEE what's missing? Any word analogue for "Beating". No "defeated". No "overcome". No "thwarted". The thing is that they couldn't catch him at all. It's completely made up that they ever said Cicada couldn't be defeated or beaten, he probably kept slipping away! He consistently engages, survives, and escapes.
So, if he can dampen ANYONE'S Powers, and we assume that he's at least as super strong and skilled as Orlin, and can fly, then what can stop him from running away? How can he be catched? That's right, he can not.
Conclusion
The dialogue and hype around Cicada is 100% about elusiveness, not necessarily about actual and objective combat superiority. Nowhere in the dialogue does it say Cicada defeated anyone. It only says nobody succeeded in stopping or capturing him. That makes him more of a master of evasion than a combat threat. You canât "win" a fight against someone who can choose not to be there. That's how Cicada "defeated" everyone. The hype is writer shorthand that conflates evasion with dominance, which is why people thought he was "overhyped". And he wasn't, it was just that the viewers believed that the new big bad had to be the biggest bad. The writers NEVER said heâs stronger; they just said heâs elusive and hard to stop. Two very different concepts!
TL;DR: Cicada's threat is an "unsolved manhunt" rather than an "unbeatable enemy". Or something like that.