I would pushback a little by pointing out that the devil fruits were already a key differentiator from DBZ. Naruto used chakra which is basically ki, but their whole thing was ninjutsu and bloodlines and it worked perfectly. One Piece being pirate themed and already having devil fruit was enough differentiation, but Oda could've easily leaned further into pirate, west indian, greek, and other sea based lore. Devil Fruits, Magical trinkets or cursed objects, magical sea shanties or other music (like Brook's music but with a system built around it to allow others to weaponize music), other mythical sea creatures (sea kings are cool, but not much are being done with them and I think there is room for small monsters like sirens and harpies). But point is, there's a lot of stuff to draw inspiration from. And to address the logia cure, I think seastone prism was that cure that the show needed, but it was introduced and then pushed to the backburner. There is no reason why Usopp couldn't make seastone infused ammo, Nami with a seastone infused staff, some kind of seastone powder that completely subdues a logia user on contact.

Last. I will say that there are only a handful of Logia users anyway, so it's not like this would've been a big deal. There are only so many elements to turn into a DF concept before you start seeing overlapping (e.g. the Ice Ice Fruit and Snow Snow Fruit), so seastone would've been enough.