I am not saying his Haki became useless, but whether he is really using them. I am 100% sure he didn’t use Haoshoku against Lucci.
I don't think he did, but I don't think he can't not use it... we saw him use it against Kaido in Gear 5.
As for FS, i simply remember how Katakuri mentioned that one needs to be focused when using it. But if drunk Kaido can use it, I can see Luffy in G5 use it too
Can definitely agree with this, it's really only if you get so upset like Katakuri that it becomes useless, but then again, just getting upset wouldn't mean you couldn't use it, I think that was just pretty much plot-device to give Luffy a shot against Katakuri at that time.
And if drunken Kaido can use FS, no reason why G5 can't use it like you said.
Pretty much, Oda can just make up any reason why something can't be used for the sake of convenience. In Water 7, he used Luffy and co. being worried about Robin as to why they lost severely to CP9 and then not so long after, it's as if they had levelled up by a 100 fold as if they didn't just lose overwhelmingly in their first encounter.
To some extent, I have stopped really looking at logic or rules as the end all be all, Oda will do whatever is necessary for the story to make it interesting even if it means breaking rules.
We're seeing people use Haki subconsciously, in their sleep, there's almost no limitation to some extent anymore at this point in the Manga.