I beat it as Oda. It's a different proposition for sure. I put a lot more archers as garrisons and made good use of diplomacy to divide my rivals and never fight alone on too many fronts.

Borderline cheating for legendary, if you can't stand being unable to save, ever.
Spoiler Alert, click show to read: 
You can alt-tab and copy the legendary autosave to another directory if you really want to try something out. Paste it back and overwrite to "load". Sometimes, you can find yourself in deep trouble because an army doesn't do what you expect it to when you tell it to move, etc. Anyway, don't use it to cheat :p