It is. Significantly.
And please don't ignore it - try to understand the problem from the perspective that in a few months the majority of Kindle users will have their devices filled with files in a format (not a DRM layer, a format) that no one is allowed to understand anymore - aside from Amazon itself.
That this was a structural decision on behalf of Amazon, and not "just a technical one". (Sure, json was so attractive to them, they practically had to remodel their entire intake infrastructure... - which by the way, you might recognize as one of the more recent arguments brought forward in the kfx thread.
I hope I dont catch any of the devs in here, any time soon, arguing, that Tim Berners Lee would have designed the web in json if he could have, because it saves 20ms rendering on every pageload - eff the peasants, or open standards, or society and its perspectives... 20ms faster load times (Amazon doesnt update eReader CPUs anymore, so I dont neglect, that there is a need...). #winning)
But back to the question at hand - "how ANY of this is inhibiting people from writing/publishing books in any way, shape, or form."
It takes away control of the "final master" from the public realm. This includes authors, publishers and the public at large.
No one but Amazon (the frigging distributer - think "Walmart") is allowed to officially produce the format, to sell it, to create in it (no specifications or tools were released), the publishing workflow was changed to adopt this new process, Amazon has never asked its customers if they want those new file properties and Amazon has not educated or even informed the public about its specifics (taking away certain rights), or even their intent to change the entire infrastructure. In fact they have buried the lead in press releases touting new features over properties fallen by the wayside.
Authors and publishers are forced to hand over the final part of what constituted "creating a book" to one company - they loose final control over typesetting, image conversion - and even "featureset" (no serifs, no hyphenations without "destroying" text integrity (soft hyphens are a workaround at best - from an archiving standpoint they can even become a problem. )).
While the public looses its ability to modify them or archive them in a format that still might be accessible a few years from now. Or to view them with anything that isnt a Amazon Kindle above a certain firmware - or to buy them in a store that isnt Amazon, or...
As you might have noticed after the Oasis release, Amazon has now also successfully linked "feature development" to their closed down file formats - while the release of the new eReader is seen as a generational turnover where no development takes place anymore.
(Devs in here probably cheered...

#winning )
Also - elborak, you might not want to agree with me, but to tell off other users - advising them not to look at the issue, to ignore it - to even call it non existent is harsh and entirely unfair. Even shortsighted.
Again - I attribute this to a very large chip on the shoulder of members of this community and the ebook blogger scene at large - for being called out for having ignored Amazons ecosystem change with the rollout of kfx. Almost entirely.
Most of them have even championed it - regardless of the cultural properties they traded away for a "new more booky font".
This is the question at hand:
Should the public be able to produce and understand, to convert and edit the dominant eBook format on the market - that's
before we talk about the necessity of DRM. Should authors and readers only be allowed access to certain layouts that increase readability - if they hand over the final production of books to one company - worldwide.
The old guard within this forum for some reason is
convinced, that it was necessary for Amazon to take those freedoms away - and that we should not talk about it at all ("so thats a straw man argument, ey?").
And I am sorry - but you have to be willing to look at details to form an understanding about what's happening here.
What this development is ushering in - is the notion of books as "content" under unified ownership - while the rest of society is just starting to realize how this turned out in other sectors.
https://www.youtube.com/watch?v=eZcygXXwM3M
If you want a more potent punchline - Amazon is currently stealing societies books ("integrating them into a closed ecosystem they control"), and some people within this community are cheering them on. In every aspect, they did it more secretively and with more malicious intent than I would have imagined any entity in this field being capable of.
From a short term profit motive it might seem in the interest of authors or publishers - but thats only if you can see yourself buying books following the "coke model", where one entity holds the "secret recipe" and you are more than happy to buy a branded product - because it comes with "exclusive features" (i.e. better readability).
I don't think people in here are too simpleminded to get this entire concept - I really dont. But for some reason a certain group in here mostly is unwilling to discuss it or even argue against it. They want to give it the "silent treatment" - while all of this is a currently ongoing process -
and the only way to argue "out of it" ("this not being a problem") is through a gateway (website login, usb transfer, a PC and significant effort - makes you able to opt into getting an older Amazon file format), entirely controlled by Amazon itself - which for a reason entirely baffling to me is accepted as a reasonable alternative and promoted in here if you'd care to ask for it.
Most people dont - so there goes the future of the ebook for at least half of its ecosystem. And don't tell me in a few years how sorry you are - tell the people in here not willing to acknowledge that - "something important changed".
Currently people within this forum try very hard to be "indifferent" and thats about it. Its a moment of hybris before you see structures collapsing... The issue doesn't go away, it just gets worse over time, as more and more people are affected.
Oh - and btw. Amazon has yet to comment on why they designed kfx this way. Blogs din't care to ask them what it was or meant in the first place (it would be interesting how they rationalized it from an organisational perspecitve).
edit: When google decided to scan the worlds books, and got sued over it, it actually produced something of value that wasnt there before. And they did provide those files in file formats that are open and every one of us can make sense of. Amazon on the other hand actually took value away and closed down an entire ecosystem. (What most people in here fail to recognize - for good (just looking at processes (who controls them) and numbers (how long until saturation)).)
Googles apks (Android App Format) can be freely created or modified by anyone who wants to, and they can even be sold on third party stores - such as, wait for it, Amazon --
yet google gets sued over infringing public interest, and Amazon gets a "high five" by every brand loyal Kindle enthusiast and his brother dev in here, while the issue is played down - don't worry - it's just the future of books.