You can always download a utility that change the unit stats (you will find it in this forum).
If you wont my opinion do not change the stats for two reasons.
1. The post marion roman troops have the power to demolish any Greek unit exept perhaps Spartan, Athenians and Corinthians Hoplites.
2. If you change the stats the game will be out of balance - meaning that the RTR team make an exelent effort to make the game as realistic as possible.
To conclude this way the game is more interesting. What is the point not fear the opponent. where is the challenge on that.
Here is the link to download the utility
https://forums.totalwar.org/vb/showthread.php?p=627109
Bookmarks