I know there has been major improvements since the Radius (radius, pickups, shape of the neck...).
[cough] uh, what? If you're asking for comparisons, you can't really know this at all. It's a personal thing of course, but the Radius guitars are far better IMO than the JS
The original Radius was in '87. It had somewhat shorter horns and shallower cutaways than the later model. In '88 the body shape was streamlined and this is the best of all three shapes. Very sleek, very sexy. Then Ibanez mad the JS
series which was a fattened up version of the Radius body. The horns got thicker. 'Bulbous' is a good word. It looks, wrong. For the last years of the Radius series, Ibanez made them just like the JS
Pickups? probably. The fred and PAF pro can be well argued to sound better than the stock dimarzios in the Radius guitars.
Neck? Preference again. I think the JS
necks are way too thick and don't fit the sleekness that the body is trying to convey. FWIW, I also think the Ultra necks on the '88+ radius guitars are too thick for those bodies. Now the '87 radius necks, ah, those were nice. I have four '88+ 540Rs and three have the '87 necks. One has a fluke '89 neck that is consistent in its taper all the way up to the body.
Trems on the radius were original Edge trems. Joe still uses those I hear although the JS
guitars come with newer models.
So in my case, the JS
is a step down.