The two Japanese X-Wings I am aware of are the Revell Takara offering and the Argonauts vinyl X-Wing. Both are tough to find. I had a Revell Takara (I acquired it for a history of SW model kits article I did for Star Wars Insider magazine in 2003, issue 75 if I recall correctly). The RT kit was more based on the Kenner toy then a studio model as it had a stubbier bottom. Plus it had a rather goofy lighting and motorization system, so it was little more then a model kit of a toy. As such, probably about the best thing for it was use as kitbash fodder for SF3D creations. Later on as the SW kit license evolved, Revell Takara also imported the MPC X-Wings to Japan.
The Argonauts kit my comparison was much better. But it was vinyl rather then styrene and as such it had some issues to deal with when building. These days, it can be expensive to acquire if somebody spots one, although it doesn't have the demand of other Argonauts issues, such as the Falcon and the Y-Wing.
Concerning the MPC kit, I have to admit it may not exactly be state of the art today. But for its time it had the potential of producing a very nice model as the accurizing work needed to make it shine really isn't all that much. It had recessed panel lines (almost unheard of back then) and was a nice size. The operating features such as the opening wings didn't work all that well. But if you glued the wings in place it did the job nicely. Add some strip styrene in spots for the gun mounts, replace the guns themselves with brass tubing, and it looks a lot better.
Looking over the details on the model, it seems pretty obvious that while MPC may not have had direct access to an ILM studio model, they certainly got at least some of the references from one (probably a pyro model). I have a 50% built X-Wing in my stash that I plan to get back to soon. I want to really trick it out and finish it alongside a 1/48 FineMolds kit for something along the lines of an "old school, new school" sort of build.
As for what makes a FineMolds model better, it mainly comes down to 3 decades of kit production advancement and improvements in research. As such, the FineMolds kit fits better and overall, the details are such that even out of the box, a great model can be built. Some people have knocked FineMolds on some details not being quite studio model accurate, or at least accurate to one specific studio model. Frankly, I don't entirely consider that fair criticism though since different scales of studio models had detail and dimension differences. As such, pinning down details to one specific model will make it less accurate to others. All things considered, while there are some minor differences, FineMolds has captured the appearance of the X-Wing in styrene form probably better then anyone else to date.