Walls has often been swings and roundabouts depending on balance, but in a situation where both teams are "equal",
Nod often has an easier time, because infiltration is far easier compared to GDI's infiltration tactics.
GDI used to lay down a high amount of vehicle pressure using Medium tanks and Mammoths. But when the Commander abilities were introduced,
Nod were able to lock down GDI vehicles far easier.
Another map that should be "balanced", look at Snow. Nod has a VERY high win rate due to the abundance of credits and the availability of EMP effects through Commander powers and LCG EMPs.
Now all of the above factors mean little if co-ordination isn't taken into account.
But in general: GDI often has better luck in large plains with a lot of choke points compared to entry paths, due to their vehicle strength. Nod succeeds where there is very few chokes or many entrances, and their fragile nature make them good at hit and run, but not in a slug-fest.