It's important to note that Peter Shinkoda is repeating what was told to him by writers of the show, who got their instructions from Loeb. He's not directly quoting or paraphrasing Loeb himself. Of course I'm not dismissing what he's saying. Just wanted to make that clarification.
This is gonna be long, and I apologise.
The thing about Iron Fist is that the character heavily emphasises the
'Mighty Whitey' trope which inherently states that white people are the best at everything, even in the arts and cultures of non-white people. Danny Rand, a complete outsider bests all of K'un-L'un's hopefuls and earns the Iron Fist. He beats people who were born for this entire purpose and come from generations of warriors. It is absurd, and the only reason why he wins is because he's a white protagonist. And the only reason why Danny is white is because he was conceptualised as an audience insert character for a demographic that largely consists of white boys and men. As much as I do like the character, this much is undeniable. Keep in mind that Danny Rand is frequently stated to be the best martial artist in the Marvel Universe, and his styles mainly consists of Asian styles.
The reason why almost no one complains about this trope is that it's just so normalised. Several books, comics, films and TV shows are have elements of this. There almost isn't any martial arts film from the 80s and 90s that didn't have this trope. It's something everyone has grown up seeing, and it's become internalised. The Karate Kid film is an example of this too, and even aside from Iron Fist there are several white male comic book characters that are masters of Asian martial arts such as Batman, Daredevil and Ninjak.
I think the problem the Iron Fist TV show had was that the just wasn't any attempt at trying to at least discuss the character's problematic history. To Doctor Strange's credit (a character that also has elements of the trope as well), the film did try to correct it in some ways by changing the Ancient One's race (which backfired because it was whitewashing -- and there is a bit in the film where Strange initially thought a stereotypically looking Old Wise Asian Master sorcerer was the Ancient One), by changing Mordo's race, by changing Wong's designation from being a man-servant to a very talented sorcerer in his own right, and by showing that all manner of people can learn the ways of the Mystic Arts. It wasn't perfect, but at least there was an attempt and I think that's why the film escaped most of the controversy.
By contrast, Iron Fist never even bothers, thinking that it would go away if it just pretended like it wasn't there. I don't think Finn Jones deserved the hate he got (he was simply showing up for a role that he fit) and the accusations of whitewashing were poorly worded, but it was problematic. Making Danny Rand Asian or part Asian would have solved a lot of problems. It immediately gets rid of the Mighty Whitey trope and can at least handle the culture appropriation aspects better (no matter what anyone says, martial arts are a part of many Asian cultures like any other nation really). Plus, it actually adds diversity to the then Defenders team which was mostly white people with the exception of Luke Cage. And it's not as if Marvel had never done any racebending before, so that wouldn't have been a big deal either. Some people try to defend keeping the character white (mind you, for just an adaptation) by saying it is racist to suggest that Asians should only be reserved for martial arts roles, but almost no one has complained about Shang-Chi and Simu Liu (except for weird nationalist Chinese online trolls that somehow think he's unattractive).
Now I think if they were gonna keep Danny white, they should have at least been prepared to have had a discussion about the problematic normalised depiction of white people stealing from non-white people. Or at least in some way, talked about Danny's privilege as a white man. But the show never has that depth or reaches that conversation, and that's why it became such a problem. Danny's characterisation doesn't help, since we know he did end up winning against Davos, took the Iron Fist, only to desert K'un-L'un when they needed him the most to avenge his parents. That's what's revealed in Season 2, but throughout both seasons he repeatedly says he never asked to be the Iron Fist, and treats it like a burden, which contradicts him choosing to win the competition instead. Then you have Davos, someone who knows how to use the Iron Fist properly, wants to be the Iron Fist and protect K'un-L'un, and is a K'un-L'un native, is instead treated as an angry and crazy villain without the sympathy characters like Vulture and Killmonger got with less screen-time. It also doesn't help that the show itself was mostly poorly written, with mediocre acting and terrible fight choreography that made Finn Jones look like an amateur.
I think that's why Jeph Loeb showing up to a comic con in a Karate gi and headband is so offensive. It's just all the insensitivity in the handling of the Iron Fist debacle exemplified in that one act of him being a white man showing up in an attire that's culturally relevant to many Asian people. It's almost like him trying to excuse adhering to a racist archetype by saying "
Hey look! I'm not racist! I love Karate!" when that's just a surface level attempt at deflection, instead of discussing and addressing the real problem. It's also why these racist comments (not to say Loeb himself is racist) aren't exactly surprising. Hollywood for as long as we know has been very comfortable using the arts and cultures of Asian people in films and putting white faces in them, only to completely disregard Asian people.