Excellent analysis on 3Speak and its centralization, this is why I have been a critic regarding the platform.
As a DTube chain block producer and co-founder of OneLoveIPFS hosting service, I have to agree on what you said, some creators don't care about decentralization as they just post their videos as a YouTube link, which can be taken down anytime. From my queries, 58.27% of the videos since 0.9 update are not IPFS uploads, which means 3rd party providers can render majority of the videos unplayable if they want to.
And yes, it does have the potential to actually be decentralized and have no single point of failure as anyone can clone the infrastructure due to its fully open source nature. For example, anyone can build (or simple make a clone) an alternative frontend that uses alternative APIs and gateways not controlled by the DTube team.
A Steem proposal to make OneLoveIPFS service free to use might be an idea to explore, but sustainability is still questionable 🤔
RE: "Decentralized" YouTube Alternatives on Steem? Nope, Not Yet | A Detailed Look at 3Speak and Dtube