He doesnt, correct but would you agree that it's far more effective with Logia-like body? So effective that Luffy didnt know why he wasnt able to hit him.
Well, I am not arguing that Katakuri used it extremely effectively. Of course he did, and that was brilliant by all aspects. But calling it completely useless is inaccurate.
As M3J also pointed out, he can stretch himself and get out of situations. Imagine an incoming attack and Luffy uses future sight to stretch his body everywhere and then all those things comeback for a full on attack. Alright, maybe not the best imagination but I am not the author and I trust Oda can do a good enough job of it. Seeing the future can be an excellent defensive technique. Katakuri even saw Pudding collapse before it actually happened, Luffy can use something like that to protect himself, his crew in excellent manner.
I think he will never have such lvl of haki that would allow him to take Mihawk's slices barehanded, however, he can always dodge them. His reflexes are insane so why add FS to it?
Protecting the crew is a good point but Oda can always prevent such moments by not exposing them to something that would need FS or he can make something else save them - Shinobu rotting earth saving them from Boro breath...
Well, if you agree that haki isn't alone enough to defend an attack from Mihawk, then you gotta agree even more that future sight is important. Yes, he can dodge them but only if he can see an attack come in. Mihawks' slice isn't slow, it can be faster than a blink and in such a scenario, future sight will allow him to dodge it.
Also, the argument has to be from within the story. Oda can do a lot of things but I don't think those can be used in an argument. If its an opinion, sure. THen I am likely to hear that FS is not something you liked as a development for Luffy. I am of the opinion that Oda should never give Franky haki, because Franky is a man of science and should use science to counter any physical limits and beyond. I am also not a fan of gear 4, but that's just an opinion. By calling it useless, you are implying that within the limits of the story, FS cannot be useful at all.
I think FS was a necessary powerup. I am sure there are other versions of CoO as well (thinking of Usopp's farsight which he awakened). This arc would require Luffy to sharpen his Kings Haki, which we've barely seen so far.