After thinking some more about those bonuses, I am convinced the game will be harder if bonuses are less dramatic. Two main reason.
1. AI wont use bonuses anyway to their best advantage (Even with better AI) so they mainly benefit the human player, sure AI use terrain but those bonus will stay the same.
2. AI use more fresh troops as they "waste" troops, the player tries to keep their troops alive and promote single "uber" units, the less powerful these uber units are the better balance between new and old.
Personally I think the large bonus is a relic of stack combat where it did not matter as much as number was more important and you could still kill a unit with enough units attacking it and with collateral damage, when you have fever units every unit is critical, if the human player can much easier get higher bonuses it just make the game to easy. Another bengif is that Terrain will also matter more and upgrading old units which the AI sucks at will also be less of a problem.
1. AI wont use bonuses anyway to their best advantage (Even with better AI) so they mainly benefit the human player, sure AI use terrain but those bonus will stay the same.
2. AI use more fresh troops as they "waste" troops, the player tries to keep their troops alive and promote single "uber" units, the less powerful these uber units are the better balance between new and old.
Personally I think the large bonus is a relic of stack combat where it did not matter as much as number was more important and you could still kill a unit with enough units attacking it and with collateral damage, when you have fever units every unit is critical, if the human player can much easier get higher bonuses it just make the game to easy. Another bengif is that Terrain will also matter more and upgrading old units which the AI sucks at will also be less of a problem.