Of course, I could be wrong. There have been westerns set in the early 20th century where the cowboys have stayed abreast of the times and that was never the decisive factor in whether it was any good or not.
Forty-six years ago, my sister was dragged by her middle school friends to see Big Jake starring 64-year-old John Wayne in the title role. Set in 1909, they had cars, motorcycles, automatic pistols, telescopic rifle sights. For all the good it did them. The movie was terrible. Considering the plot, John Wayne was way too cheerful as he tended to be in his later films, like he thought being shot in the leg or punched in the face was great fun. He addresses an overweight machete killer as "fatty".
Strange, even in Texas, that tweenagers would want to see an action film about the elderly.
In the movie, they kept referring to things as being new. "We'll have a rifle on you. With a real fine sharpshooter behind it with one of them fancy new telescopic sights."
There was The Professionals, set sometime around 1917, which had a boring middle part where nothing happened. The Wild Bunch was good, set in 1913. I saw a little of Joe Kidd on TV one time. And I liked Sergio Leone's Duck, You Sucker!
The novelty of a cowboy with a machine gun only goes so far.