This issues is interesting. I can only say my view thorough the game.
In RTW and EB Pikes dont lose formation and are able to form line at any terrain or elevation which wasnt the case in history. That makse pikes much better than legion.
On the other side Legions were much much more effective ''universal troopers'', and easier to maintain, tho sometime more expensive. In my mod I added bonuses to men and moral to legion's and bonuses for diff terrains that balances this issue a bit more.