However, most refused to play at such levels due to overall morale and who can blame them since chain rout after chain rout is hardly enjoyable (even when it's you who is routing others) and these chain routs happened over and over, I know because I saw them.
That's subjective, each morale level has different nuances and chain routing is present in all but the highest florin levels, when there's a considerable skill difference or serious mistakes. I didn't mention specifically 5k or medium flat maps or anythign else, but I did point out indirectly that habit is a strong force. Personally, I find a base mrl score 5 to be a good compromise between allowing too many errors to go unpunished and trying to control fickle events that can determine a battle. At base mrl 8, you 'll be hard pressed to find a situation where a flanking charge can rout in secs a unit that's not tired or cut from the bulk of its army.
For a more relaxed game there are higher florins settings. On lower morale a single player can rout more frequently multiple opponents, ofcourse not under any circumstances, so you usually can't be sure of the end result. And since units can rout even with few losses should a mass rout occur, the one chasing the fleeing enemy is also taking some risks when his units are getting divided. This back-and-forth game has been proven to offer an enjoyable experience for the appropriate players many a time.

On the "perfect" army, I can say that your own troops seldom guarantee you victory in all occasions, given that there are numerous examples of sword & cav armies being unable to face eastern ones even in 10k. The easier example being 10k 1v1 in a steppe map versus all cav. Or when the enemy uses his v0 alans to force you either to attack him or bring forward knight units and sustain unnecessary casualties.

Regarding mods and weak points of the VI game, like static HA, the modable stats offer you an easy and fast way to strive for a balance. With some creativity, one could make HA shoot faster than normal archers and give them more ammo, trying thus to show their ability to shoot on the run and replenish their arrow stock.