Once Upon a Time in the West was not a success when first released (the chopped-up version). It wasn’t a flop either, but it only became a smash hit when it was re-released. I worked in a cinema during the weekends in those days and they had a full house with it, day in day out, for weeks (and not only during the weekends).
About The Wild Bunch: of course it’s a visually very strong film. It has a couple of other strong points, but I guess it owes its fame mainly to its beautiful blood-letting, The action sequences were imitated by other film makers (and Peckinpah himself) over and over again. But still … it must have been one of the most discussed movies of the year, one that caused a lot of controversy (I don’t really remember, I was too young when it came out and only saw it later, in the course of the Seventies, on a late-night showing) and caused a lot of controversy. In that light it still surprises me that it wasn’t more successful, not when first released, not when re-released