I will add to this discussion:

What about the Generals with their auto regenerating units...

In my Germanian campaign I don't have any Governors, all the generals (8 of them) travel with the army and make up a formidable cavalry line which has single handedly won many battles for me... And the auto regenerate the unit over time without having to go back to a city!!

It was cool at first, but as the number of Generals grew, it has started to feel like an exploit...