I think halving the overall damage caused by the Berry Shooter's shot would help a lot. There's definitely an issue when Berry Shooters rarely use their gatling gun because it's less powerful than their regular shot. I know it has a slower shot than other Pea Shooters but that's offset by the splash damage, so you don't need accuracy.
At the moment most of the Garden & Graveyards games I'm playing are mostly filled with Berry Shooters vs All-Stars, as All-Stars seem to be the only Zombies strong enough to take them on. This is a completely different game now to before the Tactical Taco Party update, where games were more varied and characters were balanced.
I really hope EA/PopCap can sort this soon as it's really putting me off playing.