I certainly do hope Armies don't level up too fast.
The fact that an decimated army still has his full tradition, for his next full "recruitment", would mean any warmongers would always have high level armies. Take your time defeating one in your provinces, the time you take to go to theirs, it will be back full, same name, only new recruits.
We also don't know what happens to Veterans when the army they're in are defeated. I do hope they have a 50% chance at least of dieing.
The fact that agents/generals are also "hard" to kill, means that the AI will be using them for ever. And since you'e usually at war with more states, you can really have a hard time killing all thoses spies and veterans telling your own slaves to rebel.
Guess diplomacy will be more important.