That's quite a bit of good news!
I played RotS for about four years (Summer of 1549 now) today without noticing anything conspicuously egregious in the AI's actions (then again, I played far too little).

My own campaign is that of the Fukuhara Taira (holding Kyoto, Settsu and Kii and having the Sasaki of Omi and the Watanabe of Yamato as vassals). No particular inclination towards their faction, simply thought it would make a nice change to not play the scrappy upstart for once, and rather begin as the suppresive faction.
Plus, their original position is quite complex -- almost frustratingly so, especially when you don't really know what you're doing. I've decided to just sign trade agreements with everyone and develop economically (I've a plethora of neighbours).

It kind of works, now, after four years, I managed to raise a five thousand or so koku seasonal revenue by occupying two foreign trading posts (Chinese Texts and Incense), secure the allegiance of Shinmen of Tamba and of Ochi of Wakasa (why is the Clan destroyed? should it not be presented simply as Clan subdued? especially when the Clan was favoring you out of its own free will), though both times while their troops were away, so I only got the raw provinces (and as we well know, both are historically among the poorest) and I've only had Isonokami of Iga declare war on me just now -- wipped out his mainly Levy troops with my own single stack of almost only Naginata Attendants (I am trying to play to the clan's strengths which include a few bonuses for Naginata troops, plus, they seem good all-round troops, the equivalent of a terrestrial medium bune to my mind; hopefully I won't have a shock when meeting samurai). My plan was to gain the allegiance of the Kagawa in Awa and then subdue Tosa and Iyo in Shikoku, Sanuki being held by Yashima Taira already, yet I believe I wasted six turns and a few thousand koku on futile attempts already so now I am converting Iyo and hopping for better luck.

Anyway, my domain is a miserable gallimaufry right now, very difficult to defend should the diplomatic climate take a turn for the worse, yet I am very much impaired by my own vassals in developing a compact fief.
Gasp! All of those broken agreements and new wars have nothing to do with me or the 5,000 koku I happened to accidentally leave on the table while visiting!
Oh, by the by, do not think all those you shoulds were directed towards you in particular, I was writing for the generic topic reader.
The AI is doing naval invasions
You know, I am a bit annoyed by that. During SJ, I only saw the AI sending amphibious military expeditions towards me, so I thought it's just an extra "Die die die!" added by the level of difficulty, yet now I've witnessed a fleet packed with troops sent by Kitabatake in Ise against Ouchi in Nagato. And I just don't understand, is there any historical precedent for these type of maneuvers? I would understand if e.g. a fleet was sent to occupy Iwate by a clan based in Hitachi and fighting in Fukushima a daimyo holding the five northern provinces, but that never happens. Just out-of-the-blue amphibious invasions from clans half a world away, totally unsustainable should they succeed. It's very "hmmmm"...