I think the pass rates difference between Seneca and Twin Star are down more to handling than to the avionics fit - the Seneca is quite a handful, you need to look after the engines a lot more, engine failures drills are more work etc.
Yes, with a wide G1000 horizon you are less likely to end up in a turn without noticing, and there are fewer tasks where you have to look at the other side of the cockpit so you are "off scan" less often.
I would guess that a G1000 seneca would have pass rates closer to the classic seneca than to the TwinStar.