I definitely agree with you about
Once Upon A Time (I mean, it's good, but an Action movie it is not), while
Heat &
Oldboy are a Crime Drama/Revenge Thriller (speaking respectively) that just so happen to have one particularly iconic action scene in them apiece, but I think it makes a lot of sense to include
The Wild Bunch in that list. I mean, it may not be as "pure" an Action film as something like
Die Hard, but if you look at it outside the context of its Western setting, I think it has more than enough intense action in it to qualify as part of the genre, certainly more so than what else people typically thought of as "Action" movies around that time, like
The Dirty Dozen or
Bullitt, both of which had one major action scene in them apiece, and that's it.
I also think its importance to Action movies is underestimated because it primarily came from a genre (the Western) where, while the outbursts of violence are common, their portrayals tended to be pretty perfunctory, and,
like Tom Breihan wrote in his article on TWB, "the mechanics of the gunfights in, say,
Rio Bravo don’t matter as much as John Wayne’s reaction to what’s happening around him". Compare that to the final shootout in
Bunch, and how much time/effort Peckinpah obviously put into it (or even just into the first shootout), and there's a world of difference between it and the typical Westerm. Plus, its level of influence on future Action movies is undeniable, from the machine gun-driven carnage of
Rambo, the slow-motion bloodletting of
Woo, and there are even a couple of handheld cam shots in it that I would argue possibly influenced the cinematography of the
Bourne films as well, sort of making it feel like the "Rosetta's Stone" of Action movies, even though it may not be the first movie that people typically associate with the genre, you know?