You certainly add a lot of complexity to get around a 0.7V drop!
Of course one thing with the diode method is that the normal source always has to be a bit higher in voltage,so the diode is reverse biased,
This was not a problem with the TV sites,as the nominal "24V" from the mains operated supply was usually around 27-28V.
Anything voltage critical normally had a 24V to 12 V regulator in its power circuit,& other stuff like relays weren't fussy!.