Marion would be dead and the Ark would've been in Berlin where the baddies could keep trying after getting it wrong the first time.
Also without Jones they wouldn't have found the actual Ark, because they were digging in the wrong place.
I don't know who this Amy person is, but I am unimpressed. :(
boo, Amy.
So, Indiana Jones prolonged WWII. Got it.
but I don't think he had absolutely no effect on the events of the movie.
Regardless, Indy movies are less about politics and more about swash buckling action with a dash of history.
They were only digging in the wrong place because Jones stopped them from getting the headpiece of the Staff of Ra. Without Jones they get the headpiece and then dig in the right place.
Luke's motivations in RoTJ are a) becoming a full Jedi Knight; and b) his father's redemption - not his death. He achieves both of these, and Vader would not have turned from the dark side without him there.
It's an amusing idea, but I've always thought it was weird to call it a problem with the movie, as it would apply to the protagonist in a bunch of movies (spoilers abound in this extremely random assortment of movies off the top of my head):
* If Kurt Russel's character hadn't been in The Thing, everything that happened still would have happened
* If Harry and Sally hadn't been in When Harry Met Sally, New York would still be Yorking
* If Florence Pugh's character hadn't gone to Sweden in Midsommar, the tourists still would have died
* If Richard Dreyfuss's character hadn't been in Close Encounters of the Third Kind, the aliens still would have made contact, dropped off their old passengers, and picked up new passengers
* If Scott Pilgrim hadn't been in Scott Pilgrim, everyone would probably still just be hanging out more or less the same
* If Matt Damon's character hadn't been in The Martian, they would have all still ended up back on Earth
* If Rocky Balboa hadn't been in Rocky, probably two other people would have boxed and one of them would have won
To each their own, but for my money good stories are about character journeys, not about... I dunno, like, an accounting of what changed during the movie.