I think the issue is more complex than at first sight.
First, it's important not to fall into analogies with movies, which is what people often do: old movies were shot, as I said before, with fixed framings, and made to be projected on fixed (ie controled), high resolution canvas.
TV was never a fixed canvas in the 20th century, and it was low res. Not one TV showed the same image, due to variations in overscans + TV framings (manufacturers had extra plastic framings that hid x amount of visual information on the actual screen, depending on the sets).
This had two direct incidents on TV shows presentation, that were imposed on the filmmakers rather than being their original intent:
1/ they had to shoot with copious amount of dead space on all four sides, so that the show was visible with any variation in framing.
2/ they had to preserve the essential info center, (or off center, in the case of later shot Panavision shows) knowing that extractions, be it videos or 16mm, could crop any reasonable variable amount of the picture while still making the show work visually.
Also extractions were often zoomboxed by the studios so that the visuals and actors faces detail was watchable on low res TV. This resulted in ridiculous scenes, even with The X-Files first seasons, where characters sides of heads were half cropped (clearly, the same disastrous result as Pan & Scan) while they talked to another character, one nose talking to another etc.
Clearly, there was zero purity, unlike film, into these variables. The cropping wasn't an artistic intent; it was technical.
Now that old tube TV are gone (and good riddance), why should anyone keep bowing to these horrible constraints? Why should the makers keep these horrible, cropped, zoomboxed presentations that make zero sense artistically, when there is enough coverage shot on the negatives to finally have them presented proper?
If you watch the first X-Files first four seasons shows again, the image clearly feel cropped and badly as that. Just the same as Friends feel ultra-cropped too.
Bartley says he "framed" for 4/3. It means in my opinion they made sure, as still is the case today on HD shows, that nothing vital for the viewer was off the center of the frame.
It doesn't mean they composed for academy. I don't think it's viable to keep thinking that somehow, because of the format of tube TVs, Télévision series preserved the academy compositions style past the widescreen boom, for all the reasons cited above. They never used the complete top and bottom of the frame, for anything essential on those old shows, unlike anyone shooting academy did.
I was watching The Persuaders TV crew shooting a scene in the bonuses the other day, they guys did not even had marks in their viewfinder. However, all the episodes of the series crops nicely to 1.66:1 and the framings suddenly make much more sense. Even their opening credits are made with a huge focus on the center of the frame, the rest being dead empty color.
Thought there was a period of transition probably, I suggest the art of composing for 4/3 was lost some time past 1953, not only in movies (except from some arthouse movies or 16mm movies (movies produced outside of the studio system)), but also on TV shows, and especially from the 60's on.
If you look at the complete shot frame of any show from the 60's on, the way the actors are set, say for two actors talking to each other, shot from above their shoulder, reverse angle, reverse shots, clearly are just as they are in any widescreen movie shot flat. Only the sides are cropped too tight. You can see it on The Avengers comparison clip posted earlier on this thread.
So maybe you can find the odd 16mm shot TV where the whole frame is the composition and cannot be altered. This is not the case in most show listed here that have gone wide.
When you look at the widescreen framing of Mulder in the cap I posted above, the wider one make framing sense. The 4/3 one is tight and cropped.
I'm not saying the old 4/3 were wrong or invalid. They were presentations optimised for the limitations of the times.