KDE is a better understood brand than Plasma. It might always be so.
When someone says they use "KDE" as their Desktop, I still understand what they mean. After all the KDE family of applications in it's totality also represents some sort of ecosystem that one may use.
Sorry I gotta ruin your day but KDE applications means something else entirely in the KDE branding parlance: https://apps.kde.org/en-gb/ . It's a bunch of apps except Plasma and a few applications that are actually developed as part of plasma, like System Settings, Discover and a few others.
See why everyone hates this :-D ?
It would be simpler to have KDE under whatever name instead of renaming KDE to Plasma + Friends.
I find it more concerning how the author celebrates all those hypothetical device classes, instead of focusing on being good at one thing (desktops). Feels a bit like being stuck in time loop where Windows 8 is still the hottest new thing (it never was, got ridiculed from the start). But again, I might be wrong, if there are non-desktop use cases that are not only live in production but also major contributors (perhaps something like large TV brands building on/building Plasma for their UI?), then they have made all the right calls.
off topic: feels a bit weird to read through that very talkative YouTube monologue style, that's probably contributing a lot to my perception. But, wow, so much better to have a transcript than the video itself!