To be fair that's apparently the other Cicada but honestly with time travel maybe Orlin was always Cicada so fucking whatever
It's dumber when you remember that the dagger only works on dark matter meta and he's not very powerful outside of that which is why Frost wins in a straight fight
So Supergirl who bench presses buildings and spaceships and almost as fast as Barry could curbstomp him. If he flies she's as fast as Barry she could catch in a second and has super senses. Oliver can pelt him with arrows before he does anything.
Really it doesn't matter it's an excuse for Barry to be alone it's a stupid excuse but it's an excuse
Remember Cicada went missing and reappeared (more than once?) Apparently meaning Orlin Cicada was never caught, then Grace Cicada showed up down the line, which is apparently the stronger version.
So even if the League didn't exist around the time Orlin Cicada was active, he still wasn't caught. Might be the reason Team Flash is so set on curing him, so stronger versions of either Orlin or Grace Cicada won't exist in the future (which isn't totally fucking around with the timeline at all *cough*).
I know they don't like calling in heroes from other shows, but it makes no sense that he killed all these people, escapes from Team Flash for like the 10th time now and they don't ask for help. As you said, Supergirl, Arrow, The Legends or Batwoman can all take this dude. Hell, anyone of their team/sidekicks can. Call in anyone from Black Lightning and it's over in 2 minutes.
Still, future whoever Cicada better be one of the biggest bads ever if the whole league can't stop him/her.