Yeah, essentially each show seems to have Andre Kriesberg, Greg Berlanti, and an individual show runner. For Arrow, it's Marc Guggenheim. For Flash, it's Geoff Johns. For Supergirl, it'll be Ali Adler.
After Arrow season 3's premiere, it doesn't seem like Kriesberg and Berlanti had much influence as far as story credits go. While their story credits on the Flash aren't significantly higher, they're at least a scattered presence. And, frankly, it's really the only noticeable change. Arrow writers didn't leave in mass to go to Flash. The writers for Arrow are still mostly the same and the ones for Flash are new hires. It's also possible Kriesberg and Berlanti haven't left Arrow, they've just spread themselves way too thin but Flash's writers are stronger and made up for the shortfall.
I'm surprised Legends of Tomorrow isn't going to have one head writer independent of the other shows. To me, that's a bit concerning since they'll be spreading themselves even more thinly. However, it is seasons one and two of team Arrow writing it more clearly than season three's team.