IANA is recognized as an authority on global IP address allocation. See Wikipedia, or ietf.org, IANAs website, or Google it. They state that "both IPv4 and IPv6 addresses are generally assigned in a hierarchical manner," but the answers to these questions say, "the addressing is not hierarchical": Is an entirely decentralized peer-to-peer network feasible? How far could it be scaled?, What is decentralized internet? and my own previous question: Is there any logic to how IP address topology is organized globally?. Why do the answers say the exact opposite of what can be derived from basic information theory, and, of what is said by organizations that are global authorities on the topic?
You seem to assume 'The Internet' and 'IP allocation' are exactly the same thing. They aren't, not even close, yet this and your previous question seem to indicate that you either think that or want it to be so.
The Internet is very decentralized, with numerous networks interconnecting all over the globe, each network having its own local routing policy. That's why it's often called a 'network of networks'.
IP addresses are assigned by IANA to RIRs (Regional Internet Registries), which then assign them to LIRs (Local Internet Registries, often the ISPs), which in turn can assign them to their customers. That's a form of hierarchy, but it's only administrative.
This division is in no way done by dividing the available IP addresses in some logical manner based on the octets in the address. On each administrative level, blocks were assigned, returned and reassigned. To make it even more complex, IP blocks can be transferred from one owner to another, and even from one RIR tot another. So RIRs have a large number of non-contiguous IP blocks available (well, at least for IPv6, but that's a different discussion). The same goes for LIRs, which often have a fair number of blocks, from which they have assigned addresses to their customers.
In no way is there a hierarchy in the number plan, other than who's administratively responsible for sub-assignments.
So to finally answer your question, both are right, you seem to be wrong in the implications this has.
Those question you quote talk about routing/topology - how addresses and address blocks are connected. Routes are established between peers and there's no hierarchy. Each address owner/company decides by themselves with whom they peer and exchange routes.
Address allocation on the other hand is hierarchical. IANA hands out blocks to RIRs like ARIN or RIPE, who split those blocks and hand them to member companies. Those companies may split their blocks and lend them to their customers (greatly simplified).
They state that "both IPv4 and IPv6 addresses are generally assigned in a hierarchical manner.
That is the assignment for any particular company or site when it first gets IP address assignments. Even in a single large company that has been around for a long time, the addressing can get messy, especially if the company has acquired or been acquired, if the company has had to go back and get more addressing, or if the company has sold some blocks of its addressing to other, unrelated companies.
but the answers to these questions say, "the addressing is not hierarchical"
In the global Internet, the addressing is not hierarchical because connections between companies are not based on addressing. How addressing gets assigned to a company, and how that company connects its addressing to other companies with different addressing are two completely different things.
Why do the answers say the exact opposite of what can be derived from basic information theory, and, of what is said by organizations that are global authorities on the topic?
The global authorities that assign addressing to the companies that ask for addressing do not route the traffic, nor do they dictate to which other companies the recipients of the addressing can connect. The result is a giant patchwork of addressing among companies that connect to each other, that in no way resembles any order you may want.
Also, many companies have gone back to their RIR and gotten more addressing, and it is unlikely that addressing bears any relationship to the previous addressing that the company already has. Companies can merge or are acquired by other companies, sometimes between RIRs, and there is nothing requiring a company with addressing assigned by one RIR from receiving addressing from a different RIR or connecting to other companies in both the same and different RIRs.
At the end of the day, you cannot simply look at an IP address and tell where it is, nor can you tell to which other address blocks the company owning that IP address connects. Companies connect by contracts that eventually expire, and the companies are free to simply drop the connections, connect to other companies, etc. Just because Company A connects to Company B and Company C today, does not mean it must always do so, nor does it prevent Company A from also connecting to Company X, then dropping Company B and connecting to Company Y and Company Z. Some, or all of which may have been assigned addressing by different RIRs.
IANA and the RIRs do not, under normal circumstances, take back addressing from a company to which it is assigned, nor do they force a company to renumber addressing or connect to any other particular company because of addressing. The addressing is handed out, and regardless of the addressing, the companies are free to connect with whichever other companies they want to contract.
As explained in one of the answers to which you link:
The Internet is very decentralized. Each ISP connects to any other ISP it wants to, and the addressing is not hierarchical, as you seem to think. Yes, ISPs agree to get address blocks from some central authorities (RIRs), but the address blocks are not assigned in a hierarchical fashion (and with the IPv4 shortage, it gets worse as companies buy and sell address blocks to each other). For example, ISP A gets
18.104.22.168/16, and it peers with ISP B that has
22.214.171.124/22, and it also peers with ISP C that has
126.96.36.199/16. The ISP addressing may be somewhat hierarchical within an ISP (only within any one of the assigned address blocks), but between ASes, it is certainly not. AS is Autonomous System, and each is autonomous from every other AS.