Yes indeed GDI units do pack a bigger punch and have more health points then NOD units. However it boils down pretty much to the driver's skill in controlling the unit and bring it's the maximum effectiveness.A mammoth's helluava tough! Dishes out a lot of punishment and even regenerates it's hp(to half like C&C) but if just sits there and lets nod units pound it to death.
Whereas the NOD units though weaker. Are much faster and agile. And the Light tank not only fast and relatively well armored can run around the map while duking it out with it's 90mm cannon it's smaller profile makes it harder to hit then a medium or mammoth in comparasion.
HOWEVER, Nik mentioned that with a starting lumpsum of 5k person. This would definately tip the edge over to the GDI. Considering the maximum of spending you could possiblely carry into the battlefield, assuming both teams have relatively skilled players.
If everyone on the teams brought the most expensive Characters and Vehicles. The GDI would be able to spend more on Heavy mammoths while NOD would only be able to spend say 600 on a Light or 800 on a flame tank to counter em. Under the assumption that everyone can respawn with 5000 dollars even skilled veterans on the NOD side would have a difficult time trying to push back unlimited waves of Mammoths.
Hence i agree that it's more balanced to always start the game off with 0 credits.