First of all if stock the pups as supplied by Yamaki Gakki will have dual upper adjustment screws to tilt of the pup can be held in control.(..and yes,these have been claimed to have been supplied by Goto. As for how accurate that claim is,i for one have no idea-some dozen Yamaki built guitars later)
Second of all you´re right in that the OEM pups seems to have a XXXX of an output,however..this to my knowledge is not totaly the case. When you measure the Yamaki pups these will normaly be all in around 8.3-8.5k Ohms. IOW medium value humbuckers. I agree tho that the character of the OEM pups is "heavy duty",or more to the point they´re to a large degree "80s" voiced.
I´ve tried various pups in both the Washys and the Daions...and truth be told the jury´s still out with one exception. Then...that´s just me. The one type of pup that seem to be at home no matter what you toss at it with a Yamaki,and many many Mat,guitar is the P94 type.
Ie; Seymour Duncan Phatcat,GFS dream and mean 90 asf. These IMO work VERY well in maple based guitars.
That is not to say that it will be the answer to all ills but it will certainly work.
As for the OEM pups they in my experience differ quite a lot. For the sake of argument i´ve had highend wings that were totall stock sound WAY different. Likewise...Daion Power MkXX;s that all in all were supposed to be the same guitars...one was totaly "heavy metal" to the sound and the one i´ve still got around is like a glove for bluesrock as far as genre. In short,they vary. LOTS.
But as a whole these early 80s "super guitars" often carry lot of maple and that coupled with the often insane quality builds per se brings that they can be tricky to find pups for. Many times you actualy end up trying to tame the beast DOWN-in contrast to almost all other type of guitars.
Even so with my just as Yamaki built Daion Headhunter. If the OEM Yamaki pups were EVER out of place it is in a HH...just trust me on that
,it actualy IS a laughin matter cause....what WERE they thinking?
In the case of my HH i´ve replaced both the pups and pupframes with generic GFS dream 90 stuff and it absolutely work wonders. When picking non stock pups for these guitars think VERY conservative as the builds are what they are and will in a VERY noticable way add to the total package.