The non-specialist as a contrast to a specialist traces it's roots back to the inclusion of the Illusionist, and was properly codified in AD&D.
Most of those attempts were actually testbeds for some entirely absurd mechanics, like the School of Invention being a probe for Ravnica. Which is probably why UA wizards, even the ones crammed with lots of story potential like the Theurge, traditionally don't cross the approval threshold for playtest content. I'm almost entirely sure that the only reason the School of War Magic exists in print is because they had to print a Wizard Subclass for Xanathar's and they ran out of time and ideas for anything else.
And lets face it, those surveys really don't have the level of granularity that they should. The questions are basically "Do you like this?" If enough people (not most mind you, just like 30% or whatever the threshold is) answer 3/5 or less (because being good isn't good enough! it has to be loved~), the entire subclass gets totally scrapped instead of worked on. Even if the reason they didn't like it is because there was that one overpowered ability that they include just to provoke feedback, which obviously needs to be nerfed. Or this armor makes no sense out of context. Or they just don't like the Wizard class in general, so they don't care for any potential Wizard subclass to begin with.