Sea stone hand cuffs aren't technically water. I know they don't interact with devil fruits, but the abilities. Again that means that the spatial manipulation of that devil fruit is weak to haki, not spatial manipulation from other verses. The spatial manipulation from the op op fruit is weak to haki, while spatial manipulation from X-Axis from Bleach, or spatial magic from BC aren't subject to that weakness. Unless you wanna equalize haki = reiatsu which makes it worse
It's still a weakness at the end
Sea Prism stone has the "energy of the sea" or some weird plot thing around those lines.
Again, there's no "devil fruit exclusive" thing. Devil fruits just give you an ability, and how strong it is is based on the user. If a devil fruit had a limit to what it can give you, Crocodile wouldn't say the ability grows the further you train it. And Luffy's rubberiness when initially given was out of control and sloppy, without direction, but he controlled it. Oda himself stated abilities get stronger based on the user, not the fruit that gives you it.
The fruits aren't a "limit", and have no limit on what they can give you (unless it's Zoans, then your limit is obviously the beast you get). It isn't that spatial manip from Ope Ope is weak, it's that LAW himself is weaker than the Yonko, therefore his space manip from the Ope Ope doesn't work on them. If law surpasses a Yonko, his space manip would work on them in the future. (In fact one of his abilities did bypass haki when he awakened hence why he was able to use Shock Wille on Linlin)
That's why Haki's elemental intangibility negation isn't
limited to "only works on devil fruit users", because Rayleigh's quote is:
"Armament" is the sole method of combating their ABILITIES. The Devil Fruit is literally just a means of transfering the ability, not its limiter. Elemental intangibility from it isn't "Devil fruit intangibility", it's based on the element it gives you.
If you disagree, make a CRT and turn armament's elemental intangibility negation into "limited". This was discussed time and time on the wiki and the general view is that the DF is not the limit, the USER is, and Haki is, since it's literally a counter-measure ability that works against the abilities.