Maps are unbalanced, it isn't really GDI vs Nod.Mesa is unbalanced and gives GDI the advantage because the AGT covers the Tiberium Cave (inside) and the Sniper Tower.
GDI can fire on the Nod base safely with cover from the AGT, Nod doesn't get cover from the Obelisk in this manner.
Other maps with out base defense can give Nod the advantage because of Stealth Black Hand and Nuke Beacons.
Mesa is the only map that doesn't give each side a fair start, but the maps without base defense can give Nod the upper hand if GDI doesn't cover all the base enteries.