RE: what makes a board turn
I think its a bit difficult to explain why a board turns. At least its a bit to complicated for me to explain on this forum. But a simplified exaplanation is that it has to do both with rocker and outline curvature. If you check out your FSW with a long ruler, you will find it actually has a kind of gradual curve in the rear half of the board too. You can also check with the ruler closer to the rail since sometimes the v and concave profile makes the curve different close to the rail than at the "central spine". The bottom rturn in generalla quite drawn out and you don't need a lot of curve to get good action here.
Good turning is also a matter of all details of hte board coming together and working in unison for you in the turn. Maybe your current JP is just more refined in this aspect than your old one. I know the Starboard Kombat fsw boards is an extremely good bottom turner.
What makes these fsw-type boards with their flatter rockers differ from the more heavily curved EVO is that the EVO will be much easier to adjust the turning radius on. This is mostly notiecable when you try to "shorten" you bottom turn in the middle of the turn to go more vertical towards the lip. EVOs do that almost without the sailor asking for it while fsw boards takes a combination of power and technique to do it effectively. And if waves are not so powerful and sail drive is not there either, the flatter rockered boards will typically loose speed when you push them around lika that and that is why EVOs can stay so effective on the wave without having super fast rocker curves like the fsw boards.
If you want EVO performance in lighter wind than you think the 83 handles, I would look at the EVO 91 (or 07 90). Despite being big, it still turns almost as good as the smaller boards and the character of the turn is more or less the same (more similar to the 74 than the 83 though, but thats on a nitty-gritty level). To be more exact, the big EVO does on a slower wave what a smaller does on a bigger wave. The 91 is not so much more effective than the 83 when it comes to early planing(with sails up to 5.7), but it is more effective with bigger sails and of course also floatier. Due to a curvier outline if has a bit less high speed drive than the 83 but on the other hand its extremely surfy. I had quite a lot of fun on my 91 and rode it up to 2m waves (light wind) but at my 70 kilos I can as well use the 80/83 also in light wind (just loose a tad of schlogging comfort). But if you're heavier the 91 will definitely be a nice adition to your quiver. Or put differently, if you like the 83 as an allrounder, the 91 will be the perfect light wind companion.