Decentralization is not a binary characteristic. It is an architectural pattern that can be applied in varied contexts, varied degrees, toward varied goals. It is also a process. You can't decentralize something that is already decentralized. Wikipedia was a pioneer in Web 2.0. Smart contracts and decentralized apps are being referred to as Web 3.0 (So was the semantic web for a number of years, but the semantic web will likely be part of this).
Ethereum is a platform for creating decentralized applications, and it too has technology and policy that is managed by a central foundation. That doesn't mean that the ecosystem is centralized.
Zooming out, we can see that the Linux Kernel development itself has a centralized development model, even with a dictator in charge. But the Kernel is a platform for which anyone can create and ship a distribution on top of. As a result, I am able to enjoy the use of three or four distros (or more, if I wanted) that are most tailored to my use cases, instead of being forced to choose between Pepsi and Coke (Windows and OS X). And many people can get into operating system development as a hobby, with a much more achievable criteria to do so.
We can zoom out even further: The FOSS movement itself might not have existed without the relentless efforts of a few individuals over a span of many years. But from day one, the ecosystem it spawned was decentralized by design.
Going back even further, we can show that market Capitalism allowed for a rapid and diverse pace of technology and business development. Less barriers to entry. Less red tape. Obviously we have had governments, both big and small, to facilitate the economies of a nation.
What do all of these things have in common other than incorporating applied forms of decentralization? It is not just a buzzword. It is no coincidence that these frameworks have (or will) foster significant societal changes, mostly in good ways. That's not to say that the success rate is high for any given effort, but it is not a concept to be written off, especially not because of a lack of understanding of it.
The problem is that most people, even here, cannot visualize this concept in ways that they have not seen working examples of. Not a problem, not everybody is exactly a visionary in every way. But when people are actively trash talking ideas that they don't understand, without offering constructive opinions toward an understanding of it, then as technologists we ought to be taking a stand against that behavior.
Instead, what I see in many cases is that many engineers, for whatever reason, will write off certain technology ideas, believing that they understand it, when they do not. I was one of those people, for years, so I understand the mindset as good as anybody. Or perhaps they saw too many uninformed comments coming from non-technical crypto enthusiasts, and therefore have written off the idea. Folks, if this describes you, I encourage taking up the study of critical thinking techniques. The world deserves better than to have such a large number of engineers not giving the discussion a fair shake.