Arrow started as a show I barely paid attention to... to something that's actually quite thrilling. I was really into this finale, even though Ra'sh was killed far too easily given how invincible he was before that.
I love that they called in the Flash to help out... but it is awfully convenient he couldn't be around to stop the virus being released...
I'm not sure he would have been that much help.
They didn't know where or how it was going to be release and as fast as Barry Allen is, there's only one of him and it still takes time to get from place to place.
IOW no guarentee he could have stopped it or been any more effective than Team Arrow.