My first question is, why bother with the history and the product improvements from each version to the next? Just seems like a lot of work with no real result. Just my opinion.
I will try to answer your question to the best of my knowledge. The JRXT is about 10 years old. Then came the XX-T, then the XXX-T, then the MF2. I believe that's the right order. I might be missing one.
Improvements from one to the next have mostly been chassis design, width, wheel base, shock geometry, steering ackerman angles, drivetrain, slipper pad, ratios, servo mounting positions, and battery positions.
You can't buy parts anymore for the XX-T trucks and older. They've been discontinued for a few years and it's difficult to track any of them down. Parts are still made for XXX-T MF1 and MF2. There are noticeable differences between the MF1 and MF2. Such as, two mounting holes for the hinge pins for the hub carriers on the front and rear. The transmission is layed out a little differently, too. MF1 used CVDs and MF2 uses Universal. There are a few other noticable changes, too.
The difference between the XXX-T RTRI/II and MF1/2 versions are quite noticeable. The RTR versions do not come with any graphite or lightened parts. The MF1/2 come with all graphite and lightened parts. Also, the RTRII has not changed since the RTRI. The only difference there is the electronics used. The first one had better electronics. Well, a better speed control anyway. The other stuff is still the same.
Hope this information is some help to your quest in answering your LOADED questions.
Good luck