I have a question regarding the thickness of the soloist neck. I tried one out the other day and the neck felt really thick compared to other Jackson models Ive tried out, especially on the low frets. Is it thicker or is it just me?

My 2002 SL1H Soloist compared to my 1991 Fusion Std Professional: They're very similar, but the bolt on neck of my Fusion has a slightly flatter radius and is a hair or 2 thinner. I play both often and don't notice anymore. My Soloist is heavier (regarding weight \m/) and feels different for that reason too. For what it worth.... I haven't pick-up any newer examples.
(I just posted a photo elsewhere on this forum...)

Jackson necks are hand-shaped, so they are all different. This is even true of the Japanese guitars.

In general, I've found that neckthru Jacksons have thicker necks than the bolt-ons, but there's a lot of variability on both.

In order to keep costs down and for repeatability, I would expect some modern methods of manufacturing. However, I would assume final sanding to be a manual process. Fender ownership has most likely resulted in some changes. I'm only speculating....