That is all, of course, factually correct.
But why.....?
Indeed, and why does it make a difference to the fare?
Most people understood that the basic principle was to charge the same fares as London Underground on the Great Western line within zones 1-6. That's how it works on contactess and oyster, but if you want your off-peak Network Railcard discount you're presented with a fiendishly complicated menu of paper tickets, few if any of which are as cheap as they should be. It's almost as if TfL doesn't want the public to realise the Elizabeth Line is a national rail service in case they twig that they can get a third off when travelling off-peak.
I had an interesting conversation with the ticket clerk at Abbey Wood when I got back from Slough. Apparently they always sell tickets with the "underground from Ealing Broadway" restriction to destinations on the western section between West Ealing and Reading and they weren't aware of it causing any problems. The chap was firmly of the view that the wording "underground from Ealing Broadway" includes the Elizabeth Line as well as the Central and District Lines, so the ticket allows the passenger to make the whole journey on the Elizabeth Line. When I asked him if it was valid on GWR trains he thought not.
I did ask him why he would assume a passenger would wish to take a slow train to Slough in preference to a fast train to Slough after changing at Paddington and he said it was the passenger's responsibility to say if they wanted to take a fast train, which wasn't a point with which I found myself entirely in agreement.
I didn't try the ticket in the barriers at Paddington in the end, but if the people at Abbey Wood are not aware of any problems that would tend to suggest that the tickets are accepted in the barriers or, if not, the gateline staff at Paddington just let people through with these tickets. The chap said they sell a lot of them.
I'm no expert on train fares but I do have more of an understanding than the average passenger. I would argue that if I can't understand this ticket restriction, and not only that but two different, fully trained ticket office clerks working for TfL at an Elizabeth Line station can't understand this ticket restriction (or have a very different understanding than the expert members of this forum, at least), then something's not right.
It's not the fault of the people who don't understand it: it doesn't make sufficient sense.