I'm currently doing a lot of thing wrt my neck, spine and overall posture :)
I got results already , it is improving though I started from a quite rusty state. I hurt oftn but I keep the faith looking at the progress I made.
For example I may a breakthrough (fining my line or close) mostly by partly unlocking a neck which was not moving right. I would say it was like a partly "frozen" shoulder. LOts of (inner) crunchy noises later as soon as it unlocked I found my line and my body rotation and shoulder line work together on their own. Still work to do, pain but I can expect it to fix itself even in months when the issues grew in decades.
I definitely see the link between swimming and swordmanship, the spine and the shoulders can't be tight, it has to flow. Another thing that was rusty, the whole manubrium/sternum/coast pseudo articulation and the rib (proper/real) articulations with the spine. I was incredibly stiff I improve a lot on that front too. I see stronger people that are quite stiff I tend to notice those things since have done part of the work for myself.
Our culture is severely lacking and forgot lots of the wisdom some others cultures managed to preserve, we need a Renaissance :) (though that means shacking the power structure of our societies and that is another story and OT lol).