A long Mori campaign with many, many sea battles in which I've only used bow kobaya myself and I have seen a very few firebomb kobaya and heavy bunes turn up in enemy fleets - but not one medium or wako bune (the wako only ever field trade ships and are thus no threat whatsoever to my trade whereas before they were a constant menace).

There is clearly something very wrong (or right? - I am winning a low more battles on autoresolve since fielding only BKs than I did with fleets of medium bunes or bigger so maybe they are the most cost-effective naval unit) with the AI naval recruitment priorities.