Yeah, they did. But ONLY because he took every shadow he had inside himself (Shadow's Asgard). Moriah stated him passing out would do nothing to the shadows within his Zombies.
So... doesn't that mean there isn't a plot hole?
That's not actually a plot hole. Trebol and Co may or may not have watched the battle as that was never covered and you have to remember that the broadcast was cut off for a period of time.
Again Foxy ? Yeah he was disguised as Zoro
Conqueror's Haki is "invisible" and would not be visible through a screen. That said, his surprise was more due to Luffy and Doflamingo mighty.
Do you remember even Jinbei who saw him use it was surprised he could control it in Fishman Island? CoC is supposedly supposed to take more than a couple of years to learn to control which is why Joker was surprised he could actually make use of it.
Maybe he couldn't control it at that time like he can now?
I've thought of that at times too. If shanks had used haki, he would still have his arm. However, I disagree that he might not have been able to control it or that he literally decided to bet his arm on Luffy. He seemed pretty comfortable with using CoC afterwards to scare it off. I believe it was a situation where he simply jumped in to save Luffy because the situation required it. Imo, the bigger question would be why he didn't use CoA on his arm to either attack or defend. One might make the case that using CoC may require some level of concentration or so but CoA should have been a lot easier to use, especially since Shanks decided to jump in.
I thought why Shanks used CoC after his arm was bitten off was maybe similar to Luffy when he saved Ace or protected Mr. 2 from the wolves, it was used unconsciously. If Shanks was able to freely use CoC at that time then he could have used it even before that against the bandits who threatend Luffy, but he didn't.
Well, when it comes to inexperienced users, we see them show CoC when they panic or so. When shanks turned to the monster, he showed the calm angry face that experienced CoC users show. Also, if he wasn't experienced with it, the time he would have shown it was actually when the sea creature was about to attack Luffy not after he has saved Luffy. This is definitely not the face of someone who doesn't know what he's doing
Not really, we've seen Luffy & Zoro scaring a shitload of creatures without using Haki
No
This is basically what I think. That could have easily just been regular ol' "Killing Intent", which has been used a couple times in the early part of the series. I don't think Oda had haki in mind when writing the first chapter, and if he did, I doubt the idea was developed much. Definitely not to the point where it is now. He did a grand job of folding into the mythos though.