I would imagine actors and actresses (especially those associated with a show) get a salary for the year, depending on their contracted hours. Assuming those hours are filled, and they don't take advantage, I wouldn't think it out of order. Melissa has had time off from Supergirl to do her theatre stuff. Grant took some time off to get married. People hare real lives too.
I do wonder how the dagger would react to a ranged meta. I know he's not about anymore, but lets say someone like Firestorm; he's a meta, and his powers are meta powers, but they don't require close contact. Firestorm can practically shoot fireballs and flames, but would those flames … extinguish upon coming into contact with Cicada?
Thawne is a smart one. If it is his intention to indeed use the dagger, I'm sure he'll have a means of doing so. There's more tech in the future, so he'd probably know of a way to siphon the daggers power or something.
Both the Green Arrow and Supergirl should be able to defeat Cicada with ease, and if this was a small screen Justice League event, Cicada would be the worst villain for that reason alone. It does baffle me how it's clearly been stated that both Ollie & Kara tried to defeat Cicada, but couldn't - how on earth not? He's your average guy with a dagger and the ability to fly. He's not overly skilled in martial arts. Both Kara and Ollie should be able to run rings around him. Heck, even Killer Frost had the opportunity to take him down - and continues not too.
In short, Cicada is a poorly written villain by writers that probably know they've screwed up but need to meet network demands. There must've been a point during the writing of the season that the writers stopped writing, looked up at each other and one of them just said "guys, this antagonist is a joke, he's not even a threat" to which everyone agreed, only for them to realise that they were that far into the story that they couldn't backtrack.
The Flash show has had stronger and more troublesome single-episode villains than Cicada. I'm only watching at the moment because I want to see the Thawne payoff. Cicada does nothing for me as a character, threat or anything.