I'd argue that all of those photojournalism shots would still be incredible even without ANY background. They're stunning works in their own right. That's why I wrote that there will be lot of different opinions and I just wrote mine
I simply don't think the shot with Ali and Frazier would be so praised is there were no Ali and no Frazier but they were some unknown boxers. Yes, the photo is great, but I wouldn't call it incredible without capturing THAT moment. But that is what photo journalism is all about, so no offence.
I think the difference of opinion here is what makes this such an interesting hobby/job and why we get so many discussions going on this forum. What catches somebody´s attention, makes somebody want to go back and have another look, stirs emotions etc. is different from person to person. Personally I have only once returned to a photography exhibition and that was Nick Brandt´s large format portraits of African animals, where he has captured that extra IT, which makes you stop at every frame. Shot with a Pentax 6x7, normal and 2xnormal focal lengths, in B&W, but still technically close to flawless.
There are numerous photographs which captured that split second happening and are great because of that. Very few of them are technically flawless and they primarily live because of the moment they captured. Architecture, portrait, landscape, sports and wildlife photographers today need to deliver near technically perfect images, unless it´s of something extraordinary like bigfoot, a plane crashed into the building or a lion ate somebody´s wife.
Our tolerance for poorly composed, low contrast and grainy images is not what it used to be. Today, I´m sure the Ali and Frazier images would have been shot with a 1DX and a 200/2 or 300/2.8, at 12 fps and after selecting the best frame and run it through PP it would be technically flawless. Considering the equipment that photographer had at the time, that image is probably close to what was technically possible.