Alternate WW1 Scenario: Looking for feedback

[The Rock Doctor]

In a very separate writing project, I've got to consider in very broad strokes how a different WW1 might progress.

The point of departure is that General Potiorek, the Austrian governor of Bosnia, gets whacked in Sarajevo alongside Franz Ferdinand.  WW1 begins along broadly familiar lines in July and August 1914, but somebody more competent/patient than Potiorek leads the initial A-H attack against Serbia.  Serbia falls before the end of 1914, rather than generally hanging on until 1915.

This being the case, there is no real effort for the Central Powers to pull Bulgaria into the war in 1915, and no real incentive for Bulgaria to jump in, either.  It can stick to being a neutral...for a while...as can Romania and Greece.  But if any of the three do commit in the future (and I'm think maybe the Entente still entices Romania to throw down in 1916-ish), then the other two are more likely to get involved.

I assume that, overall, this is a net positive for the Central Powers and a net negative to Russia in particular, but does it have potential to significantly affect the outcome of the overall war?

[Desertfox]

Maybe Italy joins the Central Powers instead? Does it speed up the Russian Revolution? If those two happen maybe the Central Powers can win by 1917, before the US gets involved.