It seems to me that the units are overpowered as well. I did a cursory check of the units from Celtic type peoples (Aedui, Galations, etc.) and for the infantry units anyway they seem to be more powerful then even the Romans. It seems to me that the the Celts infantry units from the light,med,hvy and special units are in general more powerful then units of other factions.
I have a problem with this because the Romans and Germans consistently beat up on the Celts. It seems strange that some of the Celt units are even stronger then the elite Roman Praetorian guard. I readily admit Im not a historical scholar but as an amature historian of several readings on this period these stats dont fit.
As far as the Gaesatae are concerned I still have a problem with their stats. I know people keep saying these guy were hopped up on drugs etc. There was a study done in 2004 on drug induced volunteer and how effective they were with melee weapons. These volunteers where trained to use these weapons and when they used the drugs there effectiveness severely decreased. Granted this study used different drugs then the Gaesatae used, but if your body is numb to that much to pain I doubt the effectiveness of your abilities to use weapons. It might be a different situation if ignoring pain was due to adrenaline.

I do think the EB team did an exceptional job on this mod, I just happen to disagree with the Celt stats. If anyone has any information I could find on the Gaesatae and Celtic fighting in general, I would greatly appreciate the information.