Agreed they were way too slow and even if there was a serendipity that developed them (which would have been for no conceivable reason before people realized trench war would be a thing), then the back and forth would mean the western front is decided earlier, but the same way, and still slowly. However, there would be changes.
With Germany not taking down Russia until 1917, the Western allies would puncture the Western line in 1916 latest since German digging in would be less effective.
The biggest implication of this is that the Russian Empire would still be around, weakened by their terrible war performance. Austria will probably break into Cisleithania and Transleithania (Austria and Hungary) and italy would get some land, but without Wilson's intervention and the collapse of the country internally it wouldn't be balkanization into 8 countries. This is pre-big British ops in the Middle East, and tanks in Gallipoli seems rare, so the Turks would end up the "best" of the Central Powers relatively and lose Eastern lands to Russia, plus shreds of the Middle East. Proving themselves at Gallipoli, and Kut, if the war lasts that long, will gain them some respect, and Enver might be a hero.
As for Germany, winning in the East and losing in the West, they'd lose Alsace Lorraine and pay reparations, but ultimately a loose form of the Monarchy might survive. Without the Polish corridor, I doubt the nazis would be as popular, and I don't think hyperinflation would be as bad as RL if the war didn't last until 1918.