Yes, I've seen the marketing materials, too. The thing to think about is what you're actually using — the very next paragraph from your quote would be a good place to start:
> Specific visions for Web3 differ, but all are heavily based in blockchain technologies, such as various cryptocurrencies and non-fungible tokens (NFTs). Some visions are based around the concepts of decentralized autonomous organizations (DAOs), which seek to enable many people to have equal ownership and governance in an organization. Decentralized finance (DeFi) is another key concept, in which users exchange currency without bank or government involvement. Self-sovereign identity allows users to identify themselves without relying on a centralized authentication system like OAuth.
Note how the common thread is that these are all working around the scalability and reliability issues inherent to the popular blockchains. It's perhaps survivable for an identity system to be that slow when making changes if you don't do that very often, although it's definitely a risk for the overall network, but there's no way you're building an XMPP competitor on top of it even before you think about handling audio/video content, and privacy would of course preclude that as well.
That means that you're really building a system which looks a lot like the competitors except using something like a wallet ID to login. Beyond being rather less disruptive than the Ethereum salespeople like to tell you, that's going to look a lot like XMPP — a traditional networked service running a protocol of some level of standardization, only with a different login option. There are some natural trends which are hard to avoid: users will gravitate to the more reliable service offered by the larger companies who can invest more time in optimization, various parties will add extensions which either aren't well documented for competitors or favor their infrastructure choices, and abuse will be a problem which leads to some combination of arbitrary moats being created or users leaving to services where they don't get spam.
That last point is key: imagine if your web3 messaging startup starts to see enough usage that spammers descend en masse? Your real users will leave unless you do something about it. You can add entry fees, which will tank your user growth (which is probably already dangerously limited if you require a blockchain ID), or restrict federation to peers whom you trust to control abuse by their users.