And out of those who have played the current DH glyph at both casual and high levels, I wager most do not believe whatsoever that the play style deviates so far from the source (as you say), because it doesn't.
On this point, you're just plain wrong. Having played tank specs and having heard of Xelnath's original idea, I notice that the spec was actually built for the tanking paradigm
- that of generating resources with abilities, and then using the resources to mitigate damage.
The reason it did end up being either overpowered or underpowered simply was because there wasn't a dedicated spec on its own, with a talent and glyph system to support it at all. But that doesn't mean the basic paradigm isn't there.